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A Dictionary for Science.

compiled by:

A. J. Noice.

BSc. Hons.

Forensic Science.

edited by :

W. K. Griffiths.

BSc. Hons.

Forensic Science and Biology.

When theory and observation come together science often takes a great leap forward.

Dr. Stephen Hawking.

There are no mistakes in this work there are however hidden checks to see if it has been copied directly.

(Never download directly it doesn't take much to reword it).




AAS (atomic absorption spectroscopy) : an analytical technique based on the absorption spectrum formed when whit light is shone through a sample in the form of a vapour. The wavelengths of light absorbed are characteristic of the elements present.
ab. : abbreviation for antibody.
abatement : to lower, depreciate, or reduce. Often refers to emission reductions in air quality control.
ablastin : an antibody that inhibits the reproduction (by multiple fission) of Trypanosoma (Herpetosoma) lewisi, a parasite of the rat. This antibody appears to have no other function, e.g. it does not act as a lysin or opsonin.
ablation : the weathering of a glacier by surface melting, or rock weathering by hydraulic erosion. abiotic, those parts of a nonliving components of an ecosystem, such as air, water or temperature.
abscisic acid (ABA) : a plant hormone that inhibits cell division and promotes dormancy, interacts with gibberellins in regulating seed germination.
absolute magnitude (H10 and H0) : the brightness a comet would exhibit if placed 1 AU from both the Earth and sun. Using a special formula, the brightness estimates made for comets can be converted to absolute magnitudes which aids in the study of how a comet reacts as it approaches or recedes from the sun. For H0, an accompanying value designated "n" determines how fast a comet brightens or fades when approaching or receding from the sun.
absolute refractive index : the ratio of the velocity of light when it passes from a vacuum to another medium;

glass1.5 - 1.7
diamond 2.1
water (@ 25 o C)1.33
( click here for more indices ).

absolute temperature ( 0K ) : the lowest possible temperature ( - 273.15oC )
absorbance : a measure of the extent to which a sample in a cell absorbs light at a particular wavelength. defined as log10 ( Io/I1 ).
absorption : the uptake of small nutrient molecules by an organisms own body; the third main stage of food processing, following digestion.
absorption cross section : the measurement of an atom or molecule's ability to absorb light at a specified wavelength, measured in square cm/particle. absorption (of light), the taking in of a photon of light by an atom, molecule or ion.
absorption elution test : a test employed to identify the ABO blood group of human blood and seminal stains. The stain is fixed by dipping into boiling water and is then treated with antiserum to one of the blood groups and excess serum removed by washing. Subsequent heating in saline to 56o C eludes any antibody that has combined with the stain; if red cells of the appropriate group are then added to the eluate, they agglutinate in positive cases.
abstraction reaction : a reaction that takes any atom away from another chemical species. Classical examples in atmospheric chemistry are the gas phase removal of hydrogen from methane by hydroxyl radical or the following solution phase reaction: HSO3- + H2O 2  HSO4- +H2O
abundance : the percentage (in terms of numbers of atoms) of an isotope in a sample of an element.
acceleration by free fall (g) : the acceleration of a falling body when air resistance is neglected. Caused by gravitational attraction between the body and the Earth, it varies slightly at different points on the Earth's surface. It's standard value is 9.806 metres per second per second.
accommodation : the automatic changes made by the eye as it focuses on near objects.
accretion : the addition of air particles to hydrated drops (snow, rain, sleet, etc.) by coagulation as the drops fall through the sky.
accuracy : the closeness of measurement(s) to the true value.
acetylethylenimine : a substance used to inactivate pathogenic viruses for use as inactivated vaccines.
acervulus : fruiting body which produces conidia.
acetabularia : a single celled marine algae composed of a stalk and an umbrella like cap.
acetaldehyde (C2H4O) : This is a fairly simple aldehyde (second in the analogous series after formaldehyde) that is found in the atmosphere as a result of emissions from the manufacture of acetic acid, plastics, raw materials, and as a product in some polluted air oxidation reactions.
acetylcholine : a nitrogen containing neurotransmitter, among other effects, it slows the heart and makes the skeletal muscles contract.
acetylecholinesterase : an enzyme that hydrolyses acetylcholine to choline and acetate.
acetyl CoA : the accelerated form of coenzyme A.
acetyl CoA carboxylase : an enzyme that catalyses the carboxylation of acetyl CoA to form molonylCoA.
acetylenes : hydrocarbons with the general formula CnH2n-2, more commonly referred to as Alkynes.
acetylsalicylic acid (aspirin) : probably the commonest medicinal drug used by mankind and one of the commonest agents of suicide. In the stomach acetylsalicylic acid decomposes into aspirin, salicylic acid and acetic acid. Symptoms are nausea, although not necessarily attended by vomiting, and tinnitus. This is followed by mental confusion and hearing difficulty; sleepiness is followed by coma. Breathing is deep and slow, pulse rate high.
achondroplasia : a form of human dwarfism caused by a single dominant allele; the homozygous condition is lethal.
achromatic lens : an arrangement consisting a concave lens, or lenses, of "Flint Glass" after a standard "Crown Glass" lens which reverses chromatic abberation ( without losing all of the magnification of the first lens ).

acid : a substance which produces hydronium ions (H30+, or H+ (aq) ) in solution.
acid chyme : the acidic mixture of food and gastric juice in the vertebrate stomach.
acid-pulse (dry deposition) : deposit of powder-like substance over the ground surface; especially effecting plant leaves; that when contacted by water has a very low pH
acid rain : acidified particulate matter in the atmosphere that is deposited by precipitation onto a surface, often eroding the surface away. This precipitation generally has a pH less than 5 and sometimes much lower depending on the concentration of acidic components.
acidic solution : a solution with a pH below 7 at 25oC.
acidity constant (Ka) : The equilibrium constant for the ionisation of an acid in water.
acidophiles : Organisms that grow optimally at low pH levels and are unable to survive at "normal" levels.
aconite : a poisonous alkaloid which is found in the bulbous roots of Acontium anglicum (Monkshood). It has been used in medicine for its narcotic and analgesic properties.
aconite poisoning : from within a few minutes to an hour of ingestion the victim experiences numbness and a tingling sensation in the mouth and throat, which also become parched. With larger doses the tingling becomes a severe burning extending down the throat and to the abdomen. The tingling rapidly extends to the hands and feet, and soon the whole surface of the body is affected. The skin of the extremities is cool and clammy to the touch , but at the same time the victim will complain that they feel as though their limbs have been flayed. There is a loss of power in the legs, and sight and hearing are considerably dulled, though the victim usually remain sin full possession of their mental faculties until death ensues. Occasionally, muscular twitching is followed by convulsions, the pulse becomes weak and variable, the pupils dilated and the least exertion may bring on a fatal syncope. Death usually results from failure of the respiratory organs. Aconite paralyses all the organs in turn, and the fatal period can be from eight minutes to three or four hours.
ACP - acyltransferase : an enzyme that catalyses the transfer of an acetyl group from acetyl CoA to an acyl carrier protein (ACP).
acridine orange : dye used to identify DNA and RNA. In cells stained with it and viewed under ultraviolet illumination, DNA shows as bright green, and RNA as orange-red. Used to identify activated macrophages.
acrosome : a cap-like structure covering the head of the sperm cell; it appears to help the sperm penetrate the egg membrane due to the enzymes that it contains.
actin : a major protein component in the myofibril.
actinides : those elements from No 89 to 103 inclusive.
actinomycin : an antibiotic that inhibits transcription.
action potential : the transient change in electric potential accompanying the passage of nerve impulse.
activated lymphocyte : Any lymphocyte in an active state of differentiation. The term may therefore refer either to a lymphocyte that is proliferating on meeting antigen for the first time, or to a committed lymphocyte that is taking part in a cell-mediated immune reaction, reacting to mitogen, or developing to produce antibody.
activated macrophage : (1)A macrophage that, following differentiation and increased DNA and protein synthesis, has become more efficient at killing bacteria (such as Listeria monocytogenes) or other target cells, than the predecessor macrophage from which it derived. Products released from T lymphocytes on contact with antigen may act as macrophage activators. The term is also sometimes used to refer to the enhancement of other macrophage functions. The preferred term for cells showing such enhancement is stimulated macrophage.
activated reticular cell : A primitive reticular cell of the spleen or lymph node that has a rounded or oval nucleus with prominent pyroninophilic nucleoli (see methyl green pyronin stain) and cytoplasm flecked with basophilic or pyroninophilic particles.
activation energy : the amount of energy necessary to initiate an exergonic reaction.
activation Energy : The energy barrier that must be overcome during a collision of two potential reactants in order for a reaction to occur.
activator : a protein that switches on a gene or group of genes.
active acetylaldehyde : the complex of acetylaldehyde and thiamine pyrophosphate.
active carbon dioxide : the complex of carbon dioxide and biotin.
active formate : the formyl derivative of terahydrofolate.
active immunity : Protection due to development of an immune response in an individual following stimulation with antigen, e.g. in a vaccine or during infection
active site : the portion of an enzyme molecule into which a given substrate fits. When the active site is blocked, the enzyme cannot catalyse a reaction with it's substrate.
active transport : the movement of molecules against a concentration gradient, requiring the expenditure of energy.
activity : the number of disintegrations of a radioactive sample per second.
acute : a severe and often dangerous condition in which relatively rapid changes occur.
acute toxicity : adverse health effects occurring within a short time period of exposure to a single dose of as chemical or as a result of multiple exposures over a short time period, e.g. 24 hours.
adaptation : for an organism, any change (usually somatic) in it's structure or function, that allows the organism to better cope with conditions in the environment. For a species, any change (usually genetic, selected out by natural selection) that allows the species as a whole to better cope with it's environment.
adaptive radiation : the evolution by natural selection of a variety of types from one ancestral species.
Addison’s disease : a rare disease of the adrenal glands. It is characterised by a reduced secretion of corticosteroid hormones. This leads to weakness, intestinal upsets, darkening of the skin, low blood pressure and collapse. Formerly fatal, Addison's disease can now be easily treated with synthetic steroids.
addition reaction : a reaction in which carbon-carbon multiple bonds is broken and parts of another molecule are added to each carbon atom of the multiple bond.
adenine (A) : a purine base that occurs in animal and plant tissues as a constituent of DNA (pair with thymine) and RNA (paired with uracil).
adenohypophysis : the anterior pituitary.
adenosine diphosphate (ADP) : adenine contains two phosphate groups, one of which is bonded to the other by a high energy phosphate bond.
adenosine triphosphate (ATP) : a molecule consisting of a purine (adenine), a sugar (ribose) and three phosphate groups. A great deal of energy for biological functions is stored in the high energy bonds that link the phosphate groups, and it is liberated when one or two of the phosphates are split off from the ATP molecule. The resulting compounds are called adenosine diphosphate (ADP) and adenosine monophosphate (AMP) respectively. adhesion, the tendency of molecules of different substances to stick together.
adiabatic lapse rate : The rate of decrease of temperature with increasing altitude in the atmosphere. If heat is neither gained nor lost from the air parcel under consideration, then the lapse rate is said to be adiabatic process, any process in which heat neither enters or leaves a system. Usually such a process changes the temperature of the system. An example is the sudden compression of gas, causing its temperature to rise. The compression is assumed to take place so quickly that the gas loses none of its acquired heat.
adrenal cortex : a gland that secretes a number of steroid hormones.
adrenocorticotropin (ACTH) : a peptide pituitary hormone that stimulates the synthesis of steroid hormones by the adrenal cortex.
advection : horizontal movement of air or atmospheric properties such as temperature and vorticity to indicate the trends of that property; "horizontal convection".
advection : To transport or carry. In air quality, the rate at which particulate matter is transported.
aerobe : an organism that requires oxygen to carry on the process of respiration.
aerobic : oxygen-dependent or requiring oxygen.
aerobic Respiration : organisms utilize oxygen to break down components, derive energy, and generate needed bio molecules. Carbohydrates are cycled into water and carbon dioxide. aerobic respiration, a series of reactions for the breakdown of glucose in which the element oxygen serves as the ultimate electron acceptor.
aerosol : a colloidal suspension of liquid or solid particles dispersed in gas.
aerosol Particles : one of the components of an atmospheric air parcel, comprised of minute solids particles part of which is almost certainly water.
aerosol Scavengers : cloud droplets which attract an aerosol into snow, rain or some other water precipitate by coagulation and accretion.
AFFF ( Aqueous Film-Forming Foam ) : Fire-fighting foam which flows on burning liquid as a film, providing rapid knock-down.
afforestation : the process or act of changing land into forest by planting trees, seeding, etc. on land formerly used for something other than forestry. This can obviously be contrasted with deforestation.
agar-agar : a gelatinous substance obtained from sea-weed a solution of which in water sets to a firm jelly which is used for growing bacteria.
agglutination : the clumping of red blood cells when they are exposed to agglutinogens in blood of an incompatible type.
agglutinogen : blood substance that causes agglutination when introduced into blood of an incompatible type.
aggressive behaviour : animal behaviour in which attack is either initiated or threatened.
agonistic behaviour : the entire sequence of behavioural events in animals associated with aggressive behaviour on the part of both the aggressor and the organism against which the aggression is directed.
AIDS : acquired immune deficiency syndrome; the late stages of HIV infection; characterised by a reduced number of T cells; usually results in death caused by other diseases.
air parcel : a volume of air, the component makeup and concentrations of which remain relatively static, that tends to travel around the earth changing geographic location and position above earth as an intact unit. Air parcels can be tracked
air pollution : the contamination of the atmosphere by any toxic or radioactive gases and particulate matter as a result of human activity.
air quality assessment : a prescribed level of atmospheric pollution allowed for a certain compound during a specific time in a specific geographical area. Standards are set by some regulating body, office or agency.
albedo : reflection power or the portion of solar radiation that reaches a body (earth) surface and is immediately reflected back into the atmosphere. The uncertainty in the reflective power of clouds unfortunately increases the complexity of determining clouds' effects on modelling global warming.
albedo : a measure of the reflectivity of an object. A perfectly reflecting surface has an albedo of 1, while a black surface that absorbs all light that falls on it has an albedo of 0.
albumin : soluble proteins that remain stable in pure water.
alchemy : a pseudoscience combing practical chemistry with magical or mystical views of man and his relationship with the universe. It is the ancestor of modern chemistry and had three principle goals; the elixir of life, the universal medicine (the panacea), and the means of transmuting base metals into gold.
alcohol-resistant foam : foam for use against fires involving liquids miscible with water, e.g. alcohol, acetone.
alcohols : alkanes with a hydroxyl (-OH) group replacing one of the hydrogen atoms.
aldehyde : one of a series of organic compounds which contain a - CHO group, e.g. CH3CHO.
alga (pl. algae) : a class of eukaryotic organisms. They are primitive, mainly aquatic, non-flowering photosynthetic plants with no vascular tissue or absorbent root system.
aliphatic group : any hydrocarbon other than benzene or its derivatives.
alkali : a water soluble base.
alkali metals : the group one elements.
alkaline earth metals : the group two elements.
alkalophiles : organisms that grow optimally at high pH levels and are unable to survive below pH 8.5.
alkane : a hydrocarbon with the basic formula CnH2n+2, e.g. CH4
alkaptonuria : a relatively benign hereditary disease caused by an autosomal recessive gene. People afflicted with the disease cannot make the liver enzyme homogetistic acid oxidase, so that the intermediate compound homogentistic acid accumulates and is excreted in the urine. On exposure to air homogentistic acid is rapidly oxidised to a dark brown colour, an identifying feature of the disease.
alkenes : hydrocarbons with the basic formula , CnH2n e.g. C2H4
alkynes : hydrocarbons with the basic formula CnH2n-2, e.g. C2H2
allantois : in bird and animal embryos, an extra embryonic membrane for the storage of non diffusible nitrogenous wastes.
allele : one of two or more alternative forms of a single gene locus. Different alleles of a gene each have a unique nucleotide sequence, and their activities are all concerned with the same biochemical and developmental process, although their individual phenotypes may differ.
allometry : Study of the relationship between the growth rate of a part of an individual and the growth rate of the whole individual.
allotropes : alternative forms of an element in which the atoms are joined together in different ways, e.g. diamond, graphite and buckminsterfullerene.
Alpha (A, a) :
alpha decay : a spontaneous radioactive disintegration in which a nucleus ejects an alpha particle. This process reduces the mass number of the nucleus by four and its atomic number by two. An example is the decay of uranium 238 into thorium 234.
alpha particle : the nucleus of a helium-4 atom, consisting of two protons and two neutrons. It is extremely stable and is emitted by some radioactive nuclei in the process known as alpha decay.
alternation of generations : a characteristic of the life cycle of certain plants in which a sexual generation alternates with an asexual generation.
alto- : prefix used to define mid-level clouds.
alveolus : an air sac in the lungs, thin walled and surrounded by blood vessels. The hundreds of thousands of alveoli in each lung serve as the major vehicles for gas exchange in the mammalian body.
amelogenin : part of the first X-Y homologous gene developed by FSS used as a sex test determinant allele for the Y chromosome is 112bp in length and the X chromosome contains a 6bp deletion so is 106bp in length.
amine : compounds in which organic groups replace the hydrogen atoms in ammonia, e.g. CH3NH2, (CH3)2NH and (CH3)3N.
amino acid : the building blocks of polypeptides and therefore the basic structural unit of proteins, having the general formula ; The name amino acid is derived from the fact that a basic amino (-NH2) group and an acidic carboxylic group (-COOH) are attached to the same carbon skeleton. The R group varies from one amino acid to another, giving each amino acid it's particular characteristics. There are 20 different amino acids normally found in polypeptides.
aminoacyl-tRNA : a tRNA molecule covalently bound to an amino acid. This complex brings the amino acid to the ribosome so that it can be used in polypeptide synthesis.
aminoacyl-tRNA synthetase : an enzyme that catalyses the addition of a specific amino acid to a tRNA molecule. Since there are 20 amino acids there are 20 aminoacyl-tRNA synthetases.
amino acid sequence : the linear order of the amino acids in a polypeptide.
amino group : the NH2 group located on all amino acids that contributes certain basic (proton accepting) properties to the molecule. The amino group is able to accept a proton from a hydronium ion in the following reaction: - NH2+ H2O+ (hydronium) - NH2 + + H2O. At physiological pH (pH 7.4), most amino groups are ionised in the NH3+ form.
ammonia (NH3 ) : a highly toxic and soluble waste product resulting from the deamination of amino acids. In aquatic animals ammonia passes from the body almost continuously, so that a harmlessly low concentration is maintained. In terrestrial animals ammonia is converted into other less toxic materials, such as urea, which can be safely stored in the body until excretion.
ammonia : The molecular formula for ammonia is NH3. Ammonia is one of the most important inorganic nitrogen compounds in atmospheric water droplets. It reacts with strong acids and is one of the only known basic, gas phase atmospheric components. Atmospheric ammonia can also enhance the nucleation rate and the production of new particles in the atmosphere. These new particles can be activated to become condensation nuclei and then, through various processes, grow to a particle size of 0.05 micrometer or larger which can then be effective as cloud condensation nuclei. This process can, therefore, affect the global radiation budget. The major sources of ammonia are decaying natural organic matter, livestock wastes, fertilizers, and industrial activity.
amnion (amniotic sac) : transparent, thin but tough membrane making up the sac that encloses and protects the embryos of mammals, birds and reptiles. In humans the amniotic sac is the "bag of waters" containing amniotic fluid in which the foetus develops. It acts as a shock absorber and in other ways protects the foetus.
amoeba : a one celled organism of irregular shape that moves by extending part of its mass into temporary arm-like extensions called pseudopods.
amphoteric substance : a substance is amphoteric when it shows reactions that are characteristic of both acids and bases.
amplitude : the maximum departure from the average of oscillation.
anaemia : a state of deficiency of either the number of circulating red blood cells or the amount of haemoglobin in red blood cells.
anabolism : the build up of more complex substances from simpler ones within a living organism.
anaerobe : an organism that can carry on respiration in the absence of oxygen. Two types of anaerobes can be distinguished; facultative and obligate. Facultative anaerobes (such as yeasts) respire aerobically or anaerobically, depending upon environmental conditions. Obligate anaerobes can carry on only anaerobic respiration, regardless of whether or not there is oxygen in the environment.
anaerobic respiration : a series of reactions involving the breakdown of fuel molecules (glucose) and the generation of ATP in the absence of oxygen. The end products of anaerobic respiration can be lactic acid or alcohol, depending on the type of cell.
anaerobic respiration : living or acting in the absence of oxygen. Cellular respiration in the absence of oxygen.
analogous : term applied to body parts that are similar in function but not in structure, such as the wings of birds and bees.
analytical variability : the variability that results from repeated measurements on the same sample.
anaphase : the stage in mitosis or meiosis during which the sister chromatids or homologous chromosomes separate and migrate towards opposite poles of the cell.
androgens : general name for the various male sex hormones, or any substance that has "masculinising" effects on an organism. Testosterone is the most common naturally occurring androgen. Androgens are produced in the testes of the males and in the adrenal glands of both males and females.
anemometer : instrument used to measure wind speed.
aneuploidy : an abnormal condition in which one or more whole chromosomes of a normal set of chromosomes are either missing or are present in more than the usual number of copies.
angiosperms : a member of the group of flowering plants that have their seeds enclosed in an ovary.
angstrom(A) : unit of length used for measuring wavelengths (normally of light).
angular velocity (w) : the rate of change of angular displacement (q), i.e. w = dq/dt; it is measured in radians per second.
anion : a negatively charged ion.
anisotropic : having a physical property that is in some way dependent on direction.
animal pole : the surface of an egg close to the nucleus where the yolk density gradient within the egg is smallest.
annual (botany) : plants that flower in the same year that they are raised from seed.
anode : in an electrochemical cell (or battery), the electrode at which oxidation takes place.
anoxia : deficient supply of oxygen to tissues.
anoxic : lack of oxygen such as the inadequate oxygenation of the blood (anoxia). In aquatic environmental chemistry it refers to water that has become oxygen poor due to the bacterial decay of organic matter.
Antarctic ozone hole : recent data suggest that due to the release into the atmosphere of CFCs by human activities, the ozone hole can as large as North America during a given astral spring. The CFCs are broken apart by UV light--to form free radicals of chlorine--after they have diffused into the upper stratosphere from the troposphere. This long term movement from the troposphere to the stratosphere is possible for these chlorine containing chemicals because of there long atmospheric lifetimes; however, this type of movement is not important for more reactive species such as tropospheric ozone because of their reactivity and therefore short atmospheric lifetime. In the Antarctic stratosphere, the reaction that converts reservoir species of chlorine into an active form--which destroys ozone--takes place on the surface of particles in polar stratospheric clouds as the temperature drops below about200K. This is possible because of the unique isolation of the south polar vortex during the austral winter. The surfaces of these (nitric acid/water) clouds act as catalysts for reactions that release molecular chlorine which quickly photolyzes to chlorine's (radical) active state. It is this radical which destroys ozone.
Antarctic vortex : the combination of a drastic temperature and corresponding pressure drop along with the rotation of the Earth on its axis produces a spinning/rotating volume of air. The rotational speed of the winds commonly reaches as high as 180 mph. The motion of these winds form an impenetrable barrier such that the trapped air inside is unmixed, as it is separated from the air outside, and remains quite cold (temperatures drop below - 80 Celsius) until October. Inside the whirling volume of freezing air, the cold temperatures facilitate the condensation of gases into particles that eventually form polar stratospheric clouds anther, the part of the stamen that contains the pollen.
anthropogenic : something originating from humans and the impact of human activities on nature.
anthropogenic forcing : influence exerted on a habitat or chemical environment by humans. This obliquely refers to the idea of managed environment as opposed to a wild or non-disturbed environment. The variability of assumptions about radiative forcing can cause significant changes in the results from computer models that require an estimate of those values.
anthropology : the study of humans and their evolution.
anthropomorphism : the assigning of human characteristics to non human forms.
antibody : modified protein circulating in the serum of an animal, synthesized in response to a foreign molecule (antigen) that has entered the body.
anticodon ("nodoc") : triplet of bases on transfer RNA complementary to the codon of messenger RNA.
anticyclonic : rotation opposite the earth's rotational sense. In the Northern Hemisphere, clockwise rotation is anticyclonic. Wind in a ridge or around a high; supergeostrophic.
anticyclonic flow : the air flow produced about a high pressure center by the combination of two forces: the pressure gradient accelerating the air away from the center and the coriolos force acting inward. Anticyclonic flows are clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere.
antidepressants : substances that increase the synaptic concentrations of noradrenalin.
antigen : foreign substance (usually a protein) that stimulates formation of antibody.
antigenic determinant : the particular site or chemical group on an antigen against which an antibody is directed.
antimatter : hypothetical matter in which the constituent atoms consist of antiparticles. For every elementary particle that exists an antiparticle that is identical, except for certain of its properties, such as electric charge and is spin number, which are of equal magnitude but opposite in sign. The photon and the neutral peon are their own antiparticles. An atom of antimatter would contain a nucleus of antiprotons and antineutrinos surrounded by positrons (anti-electrons). If matter were to meet antimatter, they would annihilate each other in a burst of radiation.
antimony :
antimony poisoning : in doses of more than one grain at a time it acts as a strong emetic, this means that it may be rejected before it has time to produce a fatal effect. Where a lethal dose has been retained the victim will exhibit all the signs of having been poisoned by a strong irritant. Sensation of burning in the throat, accompanied by difficulty in swallowing. This is followed by violent pain in the stomach, incessant vomiting and diarrhoea, faintness and extreme depression, apparently provoked by the premonition of death. At the onset the pulse is accelerated, but blood pressure begins to fall and the pulse becomes slow and irregular. Perspiration is profuse and the skin cold and clammy to the touch; the extremities of the body and the face exhibit a general cyanosis. Cramps in the calves may be followed by spasmodic contraction, vertigo, and repeated syncope, until the victim finally loses consciousness and death follows from heart failure. atropine, an odourless powder, sharp to the taste, atropine is present in all the nightshades, and in its pure form is a poison capable of causing death with as little as one and a half grains. Symptoms begin with a dryness of the mouth and tongue and difficulty in swallowing. The skin is flushed, developing in a rash on the upper body; headache and giddiness give way to hallucination and then to maniacal delirium. Respiration is speedy and the pulse rapid. Later, signs of paralysis appear, passing into sleep, then coma, during which death occurs due to respiratory failure or collapse of the heart.
anti-tail : name given to a comet’s tail when it points towards the sun. This is a rare event and typically occurs when the Earth crosses the plane of the comet's orbit when that comet is relatively close to the sun and exhibiting notable tail activity.
aphelion : the point in it's orbit at which a planet or other object is at it's furthest distance from the Sun. The Earth is at aphelion on the 3rd July each year.
apical : at the top or summit.
apparent Radiant : the point from which meteors appear to originate in the sky.
apoenzyme : a protein that forms an active enzyme system by combining with a coenzyme. The apoenzyme usually has the determining effect on the specificity of the enzyme complex.
apoprotein : a protein requiring a prosthetic group for activity.
apothecium : cup-shaped, multihyphal fruiting body which produces asci.
arc minutes : an angular measure frequently used to denote the size of a comet's coma and tail. One arc minute is 1/60th of a degree.
arc seconds : an angular measure frequently used to denote the size of a comet's nuclear condensation. One arc second is 1/60th of an arc minute.
archenteron (gastrocoel) : in embryology, the hollow interior of the gastrula stage forming a primitive gut.
are (a) : unit of area equivalent to 100 square metres. The term hectare is more commonly used.
aromatic compound : an organic compound that contains a benzene ring, e.g. C6H5Cl.
argon : an element that is a member of the 8A group (Noble Gases) of the periodic table. Argon is represented by the atomic symbol Ar, has an atomic number of 18, and an atomic weight of 39.948. It is colourless, odourless, and a very inert gas. It comprises about 1% of the Earth's atmosphere.
aromatic hydrocarbons : compounds in which the carbon atoms are connected by a ring structure that is planar and joined by sigma and pi bonds between the carbon atoms. An example of an aromatic compound is benzene, C6H6
arteries : tubular branching vessels that carry blood away from the heart to various other organs.
arterioles : the smallest arteries in the circulatory system.
aryl group : an aromatic group, e.g. - C6H5.
asbestos : a naturally occurring fibrous mineral found in certain types of rock formations. The primary use of asbestos was as a fireproofing material, applied to structural steel members in multi story commercial buildings to attain proper fire protection. With its resistance to heat, asbestos was able to keep the building structure from bending and warping if exposed to fire. After widespread use of asbestos, over a 15 to 25 year time span, a pattern of illness gradually began to occur in asbestos workers. Three diseases linked to asbestos exposure are asbestosis, a fibrous scarring of the lungs, lung cancer, and mesothelioma, a cancer of the lining of the chest or abdominal cavity.
ascospore : sexual spore of an ascomycete.
ascus : sac containing ascospores.
asexual reproduction : development of new organisms without the fusion of gametes. This may occur in plants by either spore formation or vegetative reproduction. Some animals may reproduce asexually by fission or budding.
assimilation cycle : a natural process by which a water body uses microbes, which convert nonliving substances into protoplasm or cells, to purify itself from pollutants.
asteroid (minor planet) : a small non-luminous rocky body that orbits s star. Over 100,000 orbit the sun, mostly (probably about 95%) in a main belt between the orbits of Mars and Jupiter, 2.17 - 3.3 astronomical units from the sun. Of the remainder, some, such as Icarus, have highly elliptical orbits that bring them close to the sun whilst others, including the Trojan group, lie far beyond the main belt. The smallest minor planets are less than 1 km across with only about 200 exceeding 100 km; the largest is Ceres (1003 km). They are probably debris from collisions of bodies that formed between Mars and Jupiter.
astronomical unit : 1.4960 x 10 8 km, equivalent to the earth's mean orbit.
atmosphere : The sum total of all the gases surrounding the Earth, extending several hundred kilometres above the surface in a mechanical mixture of various gases in fluid-like motion. The permanent constituents are molecular nitrogen; 78.1%, molecular oxygen; 20.9%, argon; 0.934%, and approximately 0.036% carbon dioxide. Various other components exist in trace amounts. Not to be under emphasized, these trace components are where the interesting atmospheric chemistry occurs. The atmosphere can also be artificially divided into layers. Example: the troposphere (the layer closest to the earth) and the stratosphere (the layer above the troposphere).
atmosphere (atm) : the pressure of air at sea level and equivalent to 101325Nm-2 (101.325kPa).
atmosphere : the gaseous envelope around a planet.
atmospheric convection : process in which heat energy is transported through a medium, usually a gas or liquid. An example, in the atmosphere occurs when warm air with a lower density experiences an upward force until it cools and its density matches the surrounding air, generally termed convection cells.
atomic mass (of an element) : the average mass of one atom of that element in atomic mass units, symbolised (element).
atomic mass unit (m) : a very small unit of mass (1 » 1.66 x 10-24 g). atomic number (Z), the number of protons in the nucleus of one atom. In a neutral atom this is the same as the number of electrons.
atopy : hypersensitivity where tendency to allergy is inherited.
attenuation : in certain bacterial biosynthetic operons, a regulatory mechanism that controls gene expression by causing DNA polymerase to terminate transcription.
atto (a) : 10-18
ATP : adenosine triphosphate.
auger effect : the spontaneous ejection of an electron from an excited , singly charged, positive ion to form a doubly charged ion. The ion may be excited by a gamma ray from it's nucleus or by bombarding it with particles, such as photons or electrons.
austral spring : related to the Antarctic ozone depletion, south polar austral spring denotes the season of spring in the southern hemisphere when the greatest amount of ozone is lost, generally beginning in September. Astral relates to the hemisphere that the observer is currently in and the season that relates to the observer, while austral refers to the south.
auto-ignition temperature : The minimum temperature required to initiate or cause self-sustained combustion of material in the absence of any external source of energy. (Values may change significantly with geometry, gas/vapour concentration, and if catalyst is present.)
automatic cameras : cameras which use an automated focus device. This can be; i). infrared focus in which a detector emits an IR beam that is reflected from the subject back to the camera, ii). phase detection where the auto focus uses reflected light, iii). multi-beam that takes readings from a wide area, iv). continuous and predictive auto focus which allows focussing on moving objects.
autonomic nervous system : that portion of the central nervous system responsible for carrying out involuntary vital processes. The autonomic system is composed of two parts. The sympathetic system is responsible for integrating the body's many functions during an emergency. The parasympathetic system counteracts the effects of the sympathetic system. Both systems operate to some extent at all times, controlling such functions as the size of the iris diaphragm, and secretion in the stomach and duodenum.
autoradiography (radio autography) : a process whereby the location of radio-active materials is determined by use of a photographic film. When a radioactive emission (such as a b particle) hits a photographic film, it produces an exposure. In biology this process is especially useful in tracing substances throughout an organism. The organism is fed or injected with a substance containing radio-active atoms. Parts of the organism (a tissue section from the liver, or a leaf) are then exposed to film. Bright spots on the film reveal the distribution of the radio-active substance in the organ or tissue under observation. The exposed film is called autoradiograph (radio autograph).
autosomal dominant inheritance : a mechanism of inheritance of a trait that is due to a dominant mutant gene carried on a chromosome.
autosomal recessive inheritance : a mechanism of inheritance of a trait that is due to a recessive mutant gene carried on a chromosome.
autosome : any chromosome that is not a sex chromosome.
autotroph : an organism that can generate its own food supply from simple organic and inorganic elements and some external energy source such as sunlight. Green plants are autotrophes.
Autumnal Equinox : the point at which on the celestial sphere that the equator and the Ecliptic intersect. Generally the autumnal equinox occurs on or about September 21st in the northern hemisphere; this also signifies spring in the southern hemisphere.
auxotroph : a mutant strain of a given organism that is unable to synthesize a molecule required for growth and therefore must have the molecule supplied in the growth medium for it to grow.
auxotrophic mutation : A mutation that affects an organisms ability to make a particular molecule essential for growth.
Avogadro's constant (NA) : The number of objects per mol of objects (NA = 6.022 x 1023 mol -1)
Avargadro's law : The volume of a gas (of fixed pressure and temperature) is proportional to the number of moles (or molecules) of gas present, i.e. Vµn, where n is the number of moles of gas.
Avargadro's number : the number of atoms or molecules in a gram atomic weight or a gram molecular weight: 6.0226 x 1023 particles.
axis lighting : also known as oblique lighting: (Extreme Directional Lighting) The direction of the illumination, known as the angle of incidence, is the relative angle that is made by the imaginary incident light and the plane normal (perpendicular) to the surface of the target. For example oblique lighting at a 20° angle of incidence can produce the maximum contrast for textured surfaces when the viewing angle (position of the camera) is placed normal to the target. Raised textural details, such as dust or edges, will appear as bright against a dark background of the flat surface of the target.
axoplasm : the interior of a nerve fibre.


ballistics : the study of projectiles ad the extent to which their trajectories are affected by shape, propulsion systems, gravity, temperature, wind, etc. There are three branches :
interior : dealing with all aspects of propulsion within a gun barrel or at launch,
exterior : concerned with the trajectory of he projectile in flight,
terminal : relating to the effects of the missile on the target.

barbiturates : substances that inhibit NADH dehydrogenase.
baroclinic : a state of the atmosphere in which isotherms intersect isobars. The geostrophic wind results in temperature advection, and hence disturbances modify with time. Short waves are baroclinic and therefore modify.
barometric pressure : the downward pressure, at any given point in the atmosphere, of the gases directly above that point. Average pressure globally at sea level is 1,013,000 dynes per centimeter squared or 760 torr. This is defined as one atmosphere.
barophiles : bacteria which only grow at or above 40MPa or 400 atm.
barotropic : a state of the atmosphere where isotherms are parallel to isobars. (This is actually known as equivalent barotropic.) No temperature advection occurs. Long waves are barotropic.
Barr body : a highly condensed mass of chromatin found in the nuclei of normal females, but not found in the nuclei of normal male cells, which represents a cytologically condensed and inactivated X chromosome.
baryon : a collective term for nucleons and other elementary particles that have a proton or neutron in their decay products. All baryons have a quantum number called the baryon number of +1 (or -1 antiparticles).
base : a substance that accepts a proton from an acid, forming a salt and water only.
base analog : a chemical whose molecular structure is extremely similar to the bases normally found in DNA.
base pair (Kb) : two complementary bases (purine, and pyrimidine) held together by hydrogen bomds. e.g. A-T and G-C.
basicity constant (Kb) : the equilibrium constant for the ionisation of a base in water.
Beaufort scale : a scale of wind velocity, ranging from 0 (calm) to 12 (hurricane).
click here to go to scale
belladonna (extracts) :
Beer's Law (Beer-Lambert law): for monochromatic radiation, absorbance (A) is determined by the relationship: A = abc, where a = absorptivity, b = path length through the medium, and c = concentration of the absorbing species. The intensity of a ray of light which has gone through a medium.
Beer - Lambert law : The integral fraction of radiation absorbed by a sample is proportional to the number of absorbing systems (i.e. molecules) in the light path, i.e.log10 (l0/l) = e cl : where lo and l are the intensities of the incident and emerging radiation respectively : with path length of l cm of absorbing species at a concentration of c.g. mole(litre)-1. The constant e is the molar extinction coefficient in l(g.mole)-1 (cm)-1
benthic : term denoting the lower section of a surface or bottom dwelling. The largest part of all biological life are benthic organisms in the greater part of the atmosphere.
benzene : an aromatic hydrocarbon. It can be found in the air by several different ways of transmission. It can be produced for use with plastic or produced through the burning of fossil fuels. Benzene can also be found in the soil as well as some areas of groundwater pollution. Exposure to benzene has been linked to leukemia.
beta ( B, b ) : second letter of the Greek alphabet.
beta decay : radio active process in which a neutron within a nucleus decays by the weak interaction into a proton, an electron (beta-particle), and an anti-neutrino; alternatively a proton may decay into a neutron, a positron and a neutrino. Since the nuclear charge changes by one in both cases the nucleus ins changed into the nucleus of another element.
beta particle decay : radioactive process in which the atomic number, Z, of the radioactive nuclide changes but the mass number, A, does not. In electron emission, Z increases. In positron emission or in electron capture, Z decreases.
biennial : A plant which flowers only in the year following that in which they are sown.
big bang theory : An inverted extrapolation of Hubble's law which holds that the creation of the Universe began with an "explosion" of matter which is continually and infinitely expanding.
binding site : the specific portion of a molecule that binds or interacts with a substrate.
binding site mutation : the specific portion of a molecule the binds or interacts with a substrate has undergone an alteration in structure giving rise to a new allelic state.
binomial nomenclature : The system of naming a taxonomy introduced by Linneaus. Names consist of both the genus name and the species name for the organism (the genus is capitalised, the species is not, and both are italicised).
Biogeochemical Carbon : the biological and geographic study of the properties of carbon's chemical properties in relation to other reactive gases in the atmosphere.
biochemical mutation : see auxotrophic mutation.
biogenesis : The theory that all living things must be derived from other living things.
biogenetic law : A 19th century theory which held that the stages of embryological development of a given organism repeat the evolutionary stages through which the species passed. This "law" is often stated "Ontogeny recapitulates phylogeny". At present most biologists question the validity of the biogenetic law.
biological amplification or ( bioaccumulation ) : increase in concentration of DDT, PCB, and other slowly degradable, fat-soluble chemicals in organisms at successively higher levels.
biomass : the complete dry weight of organic material found in the biosphere or less strictly, the matter in the biosphere that is contained in living organisms.
biomass burning : the process of oxidizing living material. This process produces atmospheric particulates as well as the production of greenhouse and reactive tropospheric gases. These gases include CO2, CO, NOx, CH4, CH3Cl along with the addition of black carbon. All of these chemical species can be lofted relatively high in the atmosphere due to the convective heating of a fire.
biomes : large, easily distinguished community units arising as a result of complex interactions of physical and biotic factors. Grasslands or deciduous forests constitute two distinct biomes.
biosphere : a volume including the lower part of the troposphere (as high as living organisms can fly or be lofted) and the surface of the earth including the oceans. This region, by definition, encompasses all the living matter of the earth. Some very important atmospheric chemicals are produced in this region and pass into the atmosphere. This region exchanges chemicals and particulate matter with the atmosphere and soils and waters of the earth.
biosynthesis :
biotechnology/genetic engineering : recombinant DNA technology with significant applications in many areas, including plant breeding, animal breeding and medicine.
biotic community : a varied aggregate of organisms existing in common environment, less extensive biologically or geographically than a biome. Division of labour or competition for food may be internal characteristics of a biotic community.
biotic environment : The sum total of living organisms with which a given plant or animal comes into contact.
biotic potential : The inherent power of a population to increase the numbers under ideal environmental conditions.
blackbody radiation : any physical body absorbs and emits electromagnetic radiation when its temperature is above absolute zero. Planck's law determines the radiant flux of a body at a specific wavelength. In atmospheric chemistry : the calculation involving the earth's blackbody radiation shows that the earth's surface temperature would be below the freezing point of water if it did not have an atmosphere which absorbed some of the outgoing radiation.
black hole : A celestial object that has undergone such total gravitational collapse that no light can escape from it. It's escape velocity exceeds the speed of light. Once a collapsing star has shrunk to the Schwarzchild's radius it becomes a black hole.
blastocoel : the activity inside the hollow blastula stage of the animal embryo.
blastomere : a cell of the blastula in animal embryos.
blastopore : The opening of archenteron to the exterior in the gastrula stage in animal embryos.
blastula : The hollow single-layered, ball like structure forming the first identifiable phase of embryonic development in animals. The blastula is the same size as the original zygote, but it is the result of multiple cell divisions.
BLEVE ( Boiling Liquid Expanding Vapor Explosion ) : instantaneous release and ignition of flammable vapor upon rupture of a vessel containing flammable liquid above its atmospheric boiling point. blood : A fluid connective tissue composing of living cells and a non living matrix, the plasma. The blood carries oxygen, food, and waste products through the body.
blowing agent : a chemical liable to decomposition at low temperature to produce a large volume of gas.
Bohr effect : The reduction of the oxygen affinity of haemoglobin as a result of protonation.
boiling point : The temperature at which the vapour pressure of a liquid is equal to the atmospheric pressure (usually given as 1 atm. or 101.325 kPa).
bolide : a very bright meteor which fragments or explodes. Sounds of the explosion can be heard if the observer is close enough.
bolide impacts : asteroids or comets striking the earth; a possible cause of major climate changes and mass extinctions in the Earth's history.
Bolzmann's constant (k) : 1.3805 x 10-23J-1K-1
bond dissociation enthalpy (DH 0 (A-B)) : a measure of the strength of a bond. The standard enthalpy change when 1 mol of bonds are broken, all species being in the gas phase.
bond line convention : the method used to diagrammatically represent molecules without drawing in all of the atoms.
bond stretching vibrations : the oscillatory motion of two bonded atoms relative to each other. This motion consist of the two bonded atoms stretching passed their equilibrium position, then returning to their equilibrium position, and finally contracting passed their equilibrium position. The result is an increase in frequency of the bond which allows it to absorb light at that same frequency.
botany : the study of plants.
bounce lighting :
Boyles' law : the volume occupied by a fixed mass of gas at a particular temperature is inversely proportional to the pressure of the gas, i.e. V 1/P, where V is the volume and P the pressure.
brachydactyly : fingers that are abnormally short.
bract : a modified leaf beneath a flower.
bracteole : a diminutive bract.
Bragg's law :
bright band : in radar, indicates the melting point of a snowflake. High intensity return is caused by the water surrounding the ice crystal, hence appearing large.
bromochlorodifluoromethane : chemical formula CBrClF2 Synonyms: Halon 1211, Freon 12B1,chlorodifluorobromomethane. This chemical belongs to the freon family. Halon 1211 was introduced in the 1960s as an effective gaseous fire suppression agent for application in the protection of computer control rooms, museums, telecommunication switches and other areas containing highly valuable materials. Results of studies done in the late 1980s indicated that the agent was an ozone depleting chemical. Currently FM-200 and Inergen have been approved as alternatives for its use by the EPA. This chemical is stable in the troposphere but photodissociates to yield halogen radicals, which can catalytically destroy stratospheric ozone.
Bromomethane : a volatile compound with a high mixing rate in the atmosphere. Methyl bromide escapes easily into the atmosphere where it contributes to the depletion of ozone. It works similarly to CFCs in its reaction with ozone molecules (O3). In the stratosphere, with the Sun's UV light as a catalyst, methyl bromide breaks down and exchanges a bromide ion for oxygen from ozone. By breaking down the ozone molecules in the stratosphere, methyl bromide thins the ozone layer and lets more UV light pass through.
Brownian motion : three-dimensional, random movement of particles in a gas or liquid.
Brownian movement : The continuous random movements of very small particles (less than about one thousandth of a millimetre in diameter) when suspended I a fluid. It is caused by collisions between the particles and the atoms or molecules of the fluid. Brownian movement can be observed in smoke suspended in air and in a suspension of pollen grains in a liquid.
brucine :
buffer : A solution containing a weak acid and its corresponding salt, which minimises the pH changes resulting from the addition of acid or base.
bulk strain : The volume change per unit volume when a body is compressed.
bulk transport : The transportation of a large collection of molecules at one time across the plasma membrane. The processes of phagocytosis and pinocytosis are examples of bulk transport.
burns : these are categorised medically in "degrees" which depend on the severity of the tisue damage involved ;
First ; inflammation of the skin, transitory swelling and subsequent falling off of the surface layers of the epidermis.
Second ; Blisters.
Third ; Partial destruction of the true skin.
Fourth ; Total destruction of the true skin.
Fifth ; Destruction of the subcutaneous tissue and involvement of muscular tissue.
Sixth ; Extension in depth with involvement of large blood vessels, nerve trunks, serous cavities and bone.

Buys-Ballot Law : With the wind at your back, low pressure is to your left in the Northern Hemisphere.


cadaveric spasm : the stiffening that occasionally occurs at the moment of death, especially if the victim is extremely frightened or taut.
caffeine : a substance that inhibits the cyclic phosphodiesterase and causes an increase in the concentration of AMP.
calorie : the amount of heat required to raise one gram of water from 14.5 to 15.5 degrees Celsius. It is equivalent to 4.184 Joules
Calvin-Benson cycle : a cycle comprising the dark reactions of photosynthesis. It is a major part of the biochemical pathway by which green plants reduce carbon dioxide to sugars.
calyx : the outermost, usually green, envelope of a flower.
camera lucida : an instrument, usually used in conjunction with a microscope, which by means of mirrors or a prism, projects the image of an object onto a plain surface. In biology it is used to make outline drawings of objects viewed under the microscope.
candela (c) : The SI unit of luminous intensity.
cantharadin :
CAPE ( connective available potential energy ) : the amount of energy that is used by thunderstorms to create the updraft; similarly positive buoyant energy (PBE).
capillaries : the smallest blood vessels in the vertebrate body, having walls a cell thick.
capping : the addition of amethylated guanine nucleotide to the 5'end of a premessenger RNA molecule in eukaryotes; the cap is retained on the mature mRNA molecule.
carbohydrates : compounds such as sugar and starches, cellulose, glycogen, etc. containing carbon, hydrogen and oxygen, generally in a ratio that can be expressed as (CH2O)n. Carbohydrates are primary energy foods
carbon dating : when nitrogen -14 nuclei in the atmosphere are irradiated by neutrons from cosmic rays they are transformed into radioactive carbon -14 nuclei; 14N + n => 14C + p The 14C nuclei are oxidised to CO2, mix with the atmosphere and are taken up by plants or animals, where they undergo b decay to 14N. The age of material such as wood or the shell of an animal can therefore be found from the quantity of radioactive carbon atoms that it now contains. The carbon is determined by converting the material to CO2 and counting the number of b rays emitted by the gas.
Carboniferous period : a geological period of the Palaeozoic era occurring about 3.7 - 2.8 x 108 years ago. During this period land plants increased prolifically and led to the formation of the world's major coal deposits. Amphibians became more common and by the end of the period some reptiles had evolved. The Carboniferous is divided into Lower and Upper (Mississippian and Pennsylvanian). Limestone deposits were widespread in the Lower Carboniferous; millstone grits and the coal measures (alternating beds of coal, sandstone, shale and clay), in the Upper.
carbonium ions : species which contain a trivalent carbon atom with a formal positive charge.
carbon monoxide : a toxic, odourless, colourless gas produced during fossil fuel or biomass burning. Compound consisting of one carbon and one oxygen. Except for carbon dioxide, it is one of the longest lived naturally occurring atmospheric carbon compounds (this wording is meant to exclude chlorofluorocarbons). The recent change in tropospheric CO content may portend a change in the balance between oxidants and reductants in the atmosphere.
carbon monoxide poisoning : at 20% saturation the victim will experience headache, dizziness and shortness of breath if the body is exerted. 30% saturation will produce the same symptoms in a body at rest, plus nausea and cardiac throbbing. 50 - 60% will affect co-ordination and balance, and with exertion, collapse, involuntary voiding of the bowel and bladder may occur. Between 60 - 80% absorption will prove lethal. CO poisoning is cumulative so that even small amounts of the gas present in the environment it can progressively build up in the body until the onset of carboxyhaemoglobin formation. The victim will gradually become drowsy, fall into a sleep which is then followed by unconsciousness, coma and then death. The skin is pink and the body uniformly cherry red in veins, arteries and tissues. Blood is also uncommonly fluid and free from clotting. The organs are also bright cherry red and oedematous, and in the lungs the upper air packages contain a frothy liquid.
carboxylic acid : one of a series of organic compounds which contains a - CO2H group, e.g. CH3CO2H.
carcinogen : an agent (whether chemical, physical or biological) capable of increasing the incidence of malignant neoplasm’s.
carnivore : an organism whose diet consists of meat. Such organisms usually display structural adaptations for meat eating, such as sharp claws and or teeth. caroteroids, Various coloured pigments found closely associated with the chlorophyll in green plants and believed to be an accessory to the photosynthesis process.
carpel : a division in the ovary or seed vessel of a plant.
casual species : a species found in the community by accident.
catabolism : The degradation of complex organic compounds to simpler ones within living organisms or cells.
catabolite repression (glucose effect) : inactivation of an inducible bacterial operon in the presence of glucose even though the operons' inducer is present.
catalyst : any substance that lowers the activation energy of a system, allowing a given chemical reaction to proceed more rapidly. In living systems enzymes are the main catalyst.
catenane : a structure consisting of at least two circles linked as in a chain.
catastrophism : a late eighteenth and early nineteenth century idea accounting for the changes in flora and fauna indicated by fossil records. According to this idea form time to time great catastrophes destroyed all life on earth, and after each cataclysm a new special creation populated the earth with new forms of life.
cathode : in a battery or electrochemical cell, the electrode at which reduction takes place.
cation : a positively charged ion.
connective condensation level : the lowest level at which condensation will occur as a result of convection due to surface heating.
cloud condensation nuclei : particles (or aerosols) on which water condenses to form cloud drops.
celestial sphere : the imaginary sphere, of immense size, at the centre of which lies the earth and on the inner surface of which can be projected the stars and celestial bodies. The directions of these bodies, as seen from earth, are measured in terms of their angular distances from certain points and circles on the celestial sphere. These circles include the ecliptic, the observers horizon and the celestial equator where the earth's equatorial plane meets the celestial sphere. The reference points include the equinoxes, the zenith, and the celestial poles, where the earth's axis meets the celestial sphere. The earth's daily rotation causes an apparent and opposite rotation of the celestial sphere.
celibacy : abstinence from sexual intercourse.
cell : a discrete mass of living material surrounded by a membrane. The basic structural and functional unit of life in nearly all types of organisms.
cell cycle : life cycle of an individual cell. In proliferating cells the cell cycle consists of four phases: the mitotic phase (M) and a three stage interphase (G1,S and G2).
cell division : the splitting of a parent cell into two daughter cells. This phase consists of two separate phenomenon: division of the cytoplasm (cytokinesis) and division of the nucleus (mitosis). The events of nuclear mitosis follow a regular pattern of four phases; pro-phase, metaphase, anaphase and telophase. Between succeeding nuclear divisions the nucleus is in interphase.
cell membrane : the phospho-lipid bilayer forming the outer surface of every cell. The membrane is flexible, almost fluid like, and it regulates the nutrients entering the cell and the waste products or secretions leaving the cell.
cell plate : a cyto-plasmic figure formed during plant cell mitosis at the site where a new cellulose partition will be synthesised to separate the two daughter cells.
cell wall : a rigid structure composed of cellulose surrounding plant cells.
cellular metabolism : the total processes in which food and structural materials are broken down (catabolism) and built up (anabolism) within the cell.
cellulase : an enzyme capable of splitting cellulose into its monosaccharide components.
cellulose : a large, insoluble polysaccharide of repeating b -linked glucose molecules. Cellulose is the major component of plant cell walls.
Cenozoic era (or Cainozoic era) : the geological era beginning about 6 x107 years ago. It is usually taken to include both the Tertiary and Quaternary periods. During this era the mammals flourished, after the extinction of most of the reptiles dominant in the Mesozoic; the Cenozoic is sometimes known as the age of mammals. Birds and flowering plants also flourished. The Alpine orogeny took place in the earlier part of the era.
centi - (c) : 10-2
centi - Morgan (cM) : the genetic map unit. It is sometimes called a centi-Morgan in honour of T.H.Morgan.
centriole : a small deeply stained cyto-plasmic structure with a 9+0 complex of microtubules. It is thought that the centriole performs a function in cell division: however many higher plants, which seem to have no centrioles, still manage cell division.
centromere : a specialised region of a chromosome seen as a constriction under the microscope. This region is important in the activities of the chromosome during cellular division.
centrisome :
cerium (Ce) :
cervix : a "neck" of the uterus, which protrudes and opens into the vagina. chain reaction, a sequence of self sustaining reactions.
chalogens : the group six elements in the periodic table.
Charles' law : the volume of a gas (of fixed mass and pressure) is directly proportional to its temperature in Kelvins, i.e. V T, where V is the volume of gas and T its temperature in Kelvin. It can also be expressed as : Gasses expand by 1/273 of their volume at 0oC for every 1oC rise in their temperature.
characteristic species (fateful species) : Species only found in that particular community. Whilst they may not be omni-present they will not be found elsewhere.
chelex extraction : method of extracting DNA from cells. Suspensions of Chelex are alkaline and at high temperatures the results in the disruption of the cell membranes.
chemical bonds : the forces of attraction that hold two or more atoms together in a molecule. Formation of chemical bonds is thought to due to rearrangement of electron clouds.
chemical shift : in nuclear magnetic resonance, the change in resonance conditions of a nucleus caused by chemical or physical interaction with other nuclei or with electrons. chemiluminescence, the emission of light from a chemical reaction.
chemosynthesis : synthesis of organic compounds using energy derived from other chemical reactions. For example, the chemosynthesis of carbohydrates or proteins occurs in living cells using energy from the oxidation of food stuffs.
Chi ( C, c ) :
chiasma (pl. chiasmata) : the place on a homologous pair of chromosomes at which a physical exchange occurs. It is the point at which crossing over occurs.
chiasma interference (chromosomal interference) : the physical interference caused by the breaking and rejoining chromatids that reduces the probability of more than one crossing-over event occurring near another one in one part of the meiotic tetrad.
chi-square test : a statistical procedure to determine whether there is a significant difference between observed results and results expected on the basis of a particular hypothesis. ( Chi square table ).
chemical bond : the force that holds the atoms together in a molecule or the ions together in a crystalline solid. In general, atoms combine to form molecules and ions combine to form crystals in order to increase their stability by sharing or transferring outer electrons in such a way that the stable noble gas configuration results.
chlorine (Cl) :
chloroform : a heavy colourless liquid with a sweet spirituous taste and pleasant smell. It is the result of adding chlorinated lime to alcohol, and then distilling the mixture.
chlorophyll : a molecule based on the same ring structure (porphyrin) as haemoglobin, but with magnesium replacing the central ion atom. Chlorophyll is found in all green plants and gives them their colour. The molecule functions in photosynthesis by absorbing specific wavelengths of sunlight. It is know known that light raises electrons of the chlorophyll molecule to higher energy levels. As electrons return to their original level through a series of acceptor molecules, ATP is generated to serve as the direct energy source for reducing carbon dioxide to carbohydrate.
chloroplast : an organelle found in the cytoplasm of green plant cells that is the site for photosynthesis.
cholesterol : an important steroid that occurs in many membranes.
chord : a straight line joining the ends of an arc.
chorion : in intrauterine development, the outermost membrane surrounding the embryo.
chorionic villi : in mammals, projections of the chorion that extend into the uterine wall. These are outgrowths of the embryonic sac (chorion), and they provide the basis for surface exchange of materials between the mother and the very young embryo.
chromatid : one of the two visibly distinct longitudinal sub-units of all replicated chromosomes that becomes visible between early prophase and metaphase of meiosis. They are referred to as chromatids as long as they remain connected at the kinetochore.
chromatin : fragments of eukaryotic chromosomes, consisting of DNA plus histones plus non histones.
chromatography : a technique used to separate mixtures. The separation takes place on a specially selected material, e.g. aluminia.
chromosome : a structure, either linear or circular, consisting of a linear collection of genes. In prokaryotes the chromosomes consist of DNA or RNA with no proteins associated. In eukaryotes the chromosomes consist of DNA complexed with protein.
chromosome aberration : an abnormal chromosomal complement that results from loss, duplication, or rearrangement of genetic material.
chromium (Cr) :
chromosomal interference : the physical interference caused by the breaking and rejoining chromatids that reduces the probability of more than one crossing-over event occurring near another one in one part of the meiotic tetrad.
chronic : occurring for a prolonged period.
chronic toxicity : adverse health effects in a living organism resulting from repeated daily exposures to a chemical for a significant part of the organism’s life-span.
ciliated epithelium : usually incline towards the columnar shape but distinguished by the presence of minute processes which are direct prolongations of the cell protoplasm.
cilia : external cellular filaments involved in cellular mobility.
cirro- : prefix used to define high-level clouds.
cirrus : a cirri form cloud composed of ice. Appears as fibrous strands.
cis-trans (complementation) test : a test used to determine whether two mutations are within the same cistron (gene).
CJA : Criminal Justice Act.
CJA bags : a type of packaging used in certain police forces for submitting items to the FSS.
cleistothecium : ascocarp which lacks an opening.
cloning : The generation of many copies of a DNA molecule (e.g. a recombinant DNA molecule) by replication in a suitable host.
cloning vehicle ( cloning vector ) : double stranded DNA molecule that is able to replicate autonomously in a host cell and with which a DNA fragment or fragments can be bonded to form a recombinant DNA molecule for cloning.
cloud chamber : a device used to study the properties of ionising particles. It contains a chamber filled with saturated vapour. The vapour is expanded adiabatically (usually using a piston) to cool it and so make it supersaturated. When an ionising particle passes through the chamber drops of liquid condense along it's trial, thus making the trail visible.
cocaine : a powerful stimulant to the nervous system. An overdose, which could be about one gram, will over stimulate the heart to the extent that the subject will die.
coding sequence : the part of an mRNA molecule that specifies the amino acid sequence of a polypeptide during translation.
co-dominance : the situation in which the heterozygote exhibits the phenotypes of both homozygotes.
codon : the basic genetic coding unit, consisting of a sequence of three nucleotides that specify a particular amino acid to be incorporated into the polypeptide chain.
coefficient of variation : also known as the relative standard deviation and calculated using the formula:
colchicine : pale yellow crystals extracted from the meadow saffron (Colchineum autumnale) and bitter to the taste. About one third of a grain is lethal, though deaths have occurred from as little as one tenth of a grain. Symptoms do not onset for several hours, and then a burning sensation in the throat is accompanied by vomiting, stomach pains, diarrhoea and bladder spasms. Death results from paralysis of the respiratory system between 7 and 36 hours.
collagen : a protein of connective tissue.
collision and coalescence : process important in precipitation formation; involves the colliding of cloud drops or raindrops and the "sticking-together" of them.
colloid : particles of substances in solution which are smaller than those in suspensions but larger than individual molecules or ions.
colour correction of lenses : a simple lens tends to exhibit the characteristics of a prism. It breaks up light into it’s various colours and focuses them all at different points, therefore it is necessary to introduce a second element to a simple lens to create an achromatic lens which brings the different colours to focus at the same point.
columnar epithelium : epithelium formed of a cylindrical or rod shaped cells set together so as to form a complete layer, resembling, when viewed in profile, a palisade.
coma : a diffuse, luminous cloud of dust and gas that develops around a comet's nucleus as it nears the sun.
coma diameter : one of the important pieces of information an observer can determine when viewing comets. The size is usually given in arc minutes, although distant comets can display a coma that is measured in arc seconds and near-Earth comets can display a coma that is measured in degrees.
commensalism : relationship between two different species of organisms in which one derives benefit and the other suffers no harm.
common ion effect : a reduction in the concentration of a species 'AB' in solution, due to the mixture of A or B ions from another source.
competition : struggle between organisms for the necessities of life. There are two types of competition; intra-specific (between members of the same species) and inter-specific (between two or more different species).
competitive exclusion principle : also known as Gause's hypothesis, it states that two species with similar ecological requirements cannot successfully coexist.
competitive inhibitor : a substrate that reversibly combines with the active site of an enzyme and lowers the capacity of the enzyme to interact with its regular substrate.
complementation : in genetics a test to determine whether two mutations occur within the same gene or within the same cistron. If two strains have the same mutant phenotype, the mutations may occur within the same gene or in a different gene altogether. In the complementation test, two mutant chromosomes are introduced into the same cell. If mutations occur within the same gene, the mutant phenotype will still be expressed. If the mutations are in different, non-allelic genes (or different cistrons), the wild-type phenotype can be expressed, since each chromosome contains (or "compliments" for) the defective gene in the other.
complex (inorganic chemistry) : species consisting of ligands bonded to a central metal ion, e.g. [Ag (NH3)2]+.
complex repeats : several blocks of variable unit length along with more or less variable intermediary sequences.
compound : a substance consisting of atoms of different elements joined together in a definite ratio.
compound repeats : two or more adjacent simple repeats.
Compton effect : the increase in the wavelength of electromagnetic radiation when it is scattered by free electrons. The effect can only be explained by regarding the radiation as consisting of particles called photons. Part of the photon's energy is transferred to the electron, the velocity of which is thereby increased.
condensation : the change of state from vapour to liquid. The process releases latent heat.
conditional instability : a type of atmospheric instability where the air is stable if it is dry, and unstable if it is saturated.
conditioned reflex : a behaviour pattern learned through repetition of a sequence of events.
conjugate acid : species made when a base gains a proton.
conjugate base : species made when a base loses a proton.
conduction : the transfer of sensible heat from a warm object to a cool object through contact.
conidium : asexual spore.
conidiophore : hypha bearing cells which produce conidia.
contact dermatitis : inflammation of the skin due to exposure to a substance that attacks its surface.
continuous focus : the photographer may focus at any point between minimum focus and infinity. The aperture may then be adjusted to control the exposure or to control the depth of field. Depth of field scales are often printed on the camera lens barrel - especially the 35mm single lens reflex cameras. These scales may be colour coded.
conium : an oily liquid similar to nicotine and extracted from the poison hemlock (Conium maculatum). The effects of the drug are not painful, the body becomes increasingly numb until the lungs fail or the heart is paralysed. There are no post mortem signs other than those found in cases of asphyxia.
conjugation : a physical association and exchange of materials, leading to reproduction in certain organisms such as the green algae Spiro Spirogyra and the protozoan Paramecium.
constant of gravitation (G) : 6.67 x 10-11 Nkg2m-2
constant species : any species omni-present in a community but also found elsewhere.
contact trace theory : the model which states that a criminal will always carry away with them some trace from the scene of the crime, and leave some trace of their presence behind.
continuous data : a variable that can take any value within a given range of values.
control group : in a biological experiment, the organisms maintained under normal conditions to serve as a basis for comparison with the experimental group of organisms, in which some variant condition has been introduced.
convection : a transfer of heat within a fluid by fluid motions. Meteorologists refer to vertical motions as connective. Horizontal motions are advective. Also used to denote the presence of cumulus clouds (also known as connective clouds); most often refers to instability.
connective temperature : the temperature to which air must be heated to generate convection solely by heating. The air will have a dry adiabatic lapse rate from the surface to the LFC.
connective instability : the state of an unsaturated layer of air whose lapse rates of temperature and moisture are such that when lifted adiabatically to saturation, convection is spontaneous.
convergence : coming together; "piling up" of mass. Surface convergence leads to rising air whereas upper-level convergence causes subsidence.
co-ordinate (dative) bond : covalent bonds in which both electrons are donated by the same atom. They thus combine the concepts of sharing (covalent bond) and transferring (ionic bond).
co-ordination number : the number of nearest neighbours. These are ions of opposite charge in an ionic crystal, or the number of atoms that are attached to the central metal ion in a complex.
copper (Cu) :
coremium (synnema) : stalk of aggregated hyphae (conidiophores) bearing spores (conidiospores).
Coriolis force : an apparent force that makes moving objects deflect to the right of motion in the Northern Hemisphere.
corpora cavernosa : two distinct tracts of spongy erectile tissue, situated longitudinally along the length of the human penis surrounding the single, central area of erectile tissue, the corpus spongiosum.
corpus luteum : the yellow, glandular structure in mammals that develops from an ovarian follicle after the egg has been discharged (ovulated). The corpus luteum is the site of progesterone production and secretion. If the egg is fertilised, the corpus luteum persists throughout pregnancy; if the egg is not fertilised, the corpus luteum deteriorates beginning about the third week of the menstrual cycle.
corrosive : any substance that chemically attacks a material with which it has contact (body cells, materials of construction).
cortex : in plants, the storage tissue of the root or stem. In animals the outer area of an organ, such as the kidney or the brain.
cosine rule : x 2 = y 2 + z 2 - 2 yz (cos X) or Cos X = ( y 2 + z 2 - x 2 ) / 2 yz
cosmological constant : a constant devised by Einstein to add to his General relativity theory so as to allow the Universe to remain static. Later described, by Einstein, as the biggest blunder of his life.
cotyledon : the first leaf produced by a plant embryo.
coulomb (C) : the SI unit of electrical charge equal to the quantity of electricity transferred by a current of one ampere in one second.
covalent bond : where the atoms are held together by sharing pairs of electrons in their outer shells. In methane (CH4) for example, each hydrogen atom forms a bond by sharing it's only electron with one of four electrons in the outer shell of the carbon atom. Each hydrogen atom then has a pair of electrons, giving it the stable two electron outer shell of helium. The carbon atom, with four pairs of electrons in it's outer shell, has the stable eight electron outer shell of argon.
Cowper's glands : a pair of glands that lie at the base of the erectile tissue of the penis and contribute the final liquid component, a mucous alkaline secretion, to the seminal fluid.
crime stain : a sample taken directly from the crime scene, or from objects associated with it.
cristae : projections into the central matrix of a mitochondrion, produced by the repeated invaginator of the inner mitochondrial membrane and serving to increase the membrane surface area within the mitochondrion.
critical pressure : the pressure required to liquefy a substance at it's critical temperature.
critical temperature : the temperature above which a substance cannot be liquefied, whatever the applied pressure.
Cretaceous period : A geological period of the Mesozoic era, between about 13.5 and 6.5 x 107 years ago. It is divided into the Upper and Lower Cretaceous. The period saw a widespread gradual marine transgression, the rocks of the Upper Cretaceous culminating in the thick chalk deposits of Northern Europe and the Mid-Western USA. The dinosaurs and other giant reptiles, as well as the ammonites and many other invertebrates, became extinct at the end of the Cretaceous period.
crossing over : Exchange of chromosome segments between maternal and paternal chromatids during tetrad formation.
crucial experiment (critical experiment) : An experiment that distinguishes between two hypotheses by contradicting the prediction from one hypothesis while supporting the prediction from the other. It is possible to have a crucial experiment only if the two hypotheses are mutually exclusive.
cryogen : a substance used to obtain temperatures far below freezing point of water, e.g. < -78 oC.
curie (Ci) : A unit of radioactivity equal to the amount of an isotope that decays at the rate of 3.7 x 10 10 disintegrations per second.
Curie's law : The susceptibility of a paramagnetic substance is inversely proportional to it's thermodynamic temperature.
Curie point (Curie temperature) : The temperature above which a ferromagnetic substance becomes paramagnetic.
curium (Cm) :
Cushing's disease : A disorder resulting from excess corticosteroid hormones in the body. The symptoms include obesity, loss of minerals from the bones, and reddening of the face and neck; it may be associated with the symptoms of diabetes mellitus and high blood pressure. It may be caused by a tumour of he pituitary gland or the adrenal gland or by prolonged therapy with high doses of corticosteroids: the treatment is determined by the cause.
cutin : The waxy secretion from leaf epidermal layers that forms leaf cuticle.
cyanide : Fifty grams is sufficient to cause death within five minutes by an inhibition of the bloods capacity to absorb oxygen.
cyclonic : Rotation in the same sense that the earth rotates, counter-clockwise in the Northern Hemisphere. Wind around a low; sub-geostrophic.
cytosine : A base found in DNA and RNA. Abbreviated C for the free base, rC for cytidine, and dC for deoxycytidine.
cytochrome : A molecule in the respiratory assembly with the characteristic porphyrin ring structure found also in haemoglobin, myoglobin and chlorophyll. By contrast with haemoglobin, in cytochromes the central iron atom is easily oxidised and reduced. This allows the cytochrome to pass electrons in the electron transport chain.
cytokines is : Cytological changes, usually occurring along with mitosis, through which the cytoplasm of one cell is divided to form two cells.
cytology : The study of cells.
cytoplasm : All the liquid colloid material in the cell that is enclosed within the plasma membrane, excluding that of the nucleus. Cell organelles reside in the cytoplasm of the cell.


dalton: a unit of molecular weight, the mass of a hydrogen atom. It is also known as an avogram.
Dalton's law of partial pressures: the total pressure of a gas mixture is the sum of the partial pressures of the individual gasses in the mixture. The partial pressure of a gas in a mixture being defined as the pressure that that gas would exert if it occupied the container alone, i.e. PT = PA+ PB+ PC..... where PT is the total pressure of the mixture and PA, PB, PC are the partial pressures of the gasses in the mixture.
dangerous substances (UK): Defined substances which may be hazardous to the fire services in an emergency. (Dangerous Substances (Notification and Marking of Sites) Regulations 1990). Defined substances over which control is exercised for conveyance in all road tankers or in tank containers >3m capacity. (The Dangerous Substances (Conveyance by Road in Road Tankers and Tank Containers) Regulations 1981). Defined substances covered by a comprehensive system to inform consumers of potential dangers and to reduce the hazard when carried by road. (The Classification, Packaging and Labelling of Dangerous Substance Regulations 1984). Defined substances, including all toxic gases, all flammable gases, asbestos and most hazardous waste, for which carriage in packages or in bulk is controlled. (The Road Traffic (Carriage of Dangerous Substances in Packages etc.) Regulations 1986).
dansyl chloride: A chemical that reacts with the amino groups of proteins to form a highly fluorescent compound.
DDT: Para-dichlorodiphenyltrichloroethane was commonly used during the second World War. It was used to kill mosquitoes that carried malaria and yellow fever and it was also used to kill body lice that can transmit typhus. Many problems have been associated with the use of DDT. Some of these problems are the bioaccumulation in the food chain, decline of smaller animals, and softening of bird’s eggs. In 1973 the EPA banned all use except those essential to public health. DDT is still being used extensively in developing countries.
daylight stream: a meteor stream that is active and above the horizon at the same time as the sun. They can normally only be observed by radar and radio-echo techniques.
deamination: the removal of the amino group (-NH2) from an amino acid by chemical oxidation.
de Broglie wave: a wave associated with any moving elementary particle with non-zero mass, since such particles exhibit wave properties under appropriate conditions. For example they may be diffracted by a crystal lattice. The de-Broglie wavelength of a particle mass (m) and velocity (v) is h/mv where h is Plank's constant.
deca (da): 101
decay constant (k): the rate constant (first order) for the decay of a radio nucleotide.
deci (d): 10- 1
decibel (db): a unit used to compare power levels on a logarithmic scale. It is one tenth of a bel but this unit is rarely used. Two power levels differ by n decibels when n = 10log10 P/P0. The unit is often used to express a sound intensity in which case P0 is usually taken as the intensity of the lowest audible note of the same frequency as P.
deciduous: a plant that sheds it's leaves.
declination (DECL): the celestial equivalent of latitude. The celestial equator is zero degrees, while the celestial north and south poles are 90 and -90 degrees, respectively.
de-differentiation: the reversion of a cell from a condition of specialisation to a non specialised, embryonic type of state, as is often the case in cancer cells.
deductive logic: a process whereby a conclusion is reached by proceeding from a generalisation to specific instances.
deforestation: type of "forestry practice" which involves the permanent removal of forests and their undergrowth so that the land can serve another purpose. This practice has had a profound effect on global environmental problems (air pollution, global warming), soil erosion, desertification, sedimentation of water courses, alteration of climate and hydrological cycles, alteration of the atmospheric oxygen and carbon dioxide balance and has caused many species to become extinct, reducing worldwide biodiversity. A common deforestation practice is to simply burn the forest while clearing the land for a seasonal crop. This also creates a large-scale release of carbon dioxide further compounding the global warming effect. Since most of the available nutrients are contained in the forest biomass the newly cleared land does not support a crop for more than a few seasons before adjacent land must be deforested.
degradation: the process of breaking down complex molecules to simpler ones, generally accompanied by a liberation of energy. Can also refer to the loss of quality, integrity or character of DNA i.e. breakdown of DNA into smaller fragments by chemical or physical means.
dehydration synthesis: the joining together of small units (such as amino acids or glucose) into a single large molecule by the elimination of water. One of the units contributes the H+, the other the OH-.
degree of condensation (DC): a term used to denote how the comet's surface brightness is concentrated within the coma. A DC of 0 indicates the comet surface brightness is evenly distributed with no apparent concentrated. A DC of 9 indicates the comet essentially looks like a planet.
deionised water: pure water obtained by passing tap water through an ion-exchange resin.
deletion: the loss of a segment of a chromosome during cross over, resulting in the developing organism. Such aberrations can provide significant clues in the mapping of gene loci.
delocalisation: the 'spreading out' of electron density over a molecule or ion.
delta ( D, d ): fourth letter of Greek alphabet.
denature :the process by which the molecular structure of a substance is artificially altered i.e. the separation of double stranded DNA into single stranded DNA by heat or chemical means.
denitrification: a step in the nitrogen cycle which involves the reduction of nitrates into nitrite, nitrous oxide, ammonia or elemental nitrogen. It is carried out by certain forms of denitrifying bacteria in the soil and serves as an important part of the breakdown of dead organism. It is responsible for the loss of much of the soil's natural and synthetic fertilizers. This process is favoured most in warm, anaerobic conditions.
density: The mass per unit volume of a substance measured in kilograms per cubic metre, in these units water has a density of 1000kg m-3.
density dependent factors: Factors operating on individuals to limit or reduce a population when it reaches some critical size. Density-dependent factors include physiological or behavioural changes in individuals which cause migration, reduced mating practices, etc.
deoxyribose: The five carbon sugar present in DNA (deoxyribonucleic acid).
dermis: The deep layer of the skin where the cells produce fibres made of the protein collagen with these fibres criss-crossed in a felt like mat.
desiccate: To dry out by losing water.
detonation: explosion in which the flame-front advances at more than supersonic velocity.
detritivore: Organisms that eat dead and decomposing things. Most fungi are detritivores, as are many bacteria and prokaryotes.
Devonian period: A geological period of the Upper Palaeozoic era, lasting from about 4.15 to 3.7 x 108 years ago. It is divided into seven stages, based on invertebrate fossil remains, such as corals, brachiopods, ammonoids, and crinoids. The rocks containing these fossils were marine deposits but the Devonian period also shows extensive continental deposits (Old Red Sandstone). Fossils from these rocks include fish, land plants, and fresh water molluscs.
dew point (Td): the temperature at which air is cooled enough to reach its saturation point (100% humidity) for a given volume of water vapour in the air. If the air cooling occurs because of adiabatic expansion, clouds are formed; if it is due to contact of the air with a colder object, condensation (known as dew) is formed on the object; and if it is due to mixing of a warmer, moist air parcel with a cooler, dry parcel, fogs and condensation trails are created. Unlike humidity, the dew point is not based upon the temperature or pressure of the air, but solely upon the water vapour content. It can be measured using a dew point hygrometer, from the known temperature and relative humidity and by measuring the difference in wet and dry bulb temperatures. It is of importance in predicting fogs, frost, dew and overnight minimum temperatures.
diabetes: A group of diseases in which the insulin effect is inadequate for the uptake of glucose from the blood.
dialysis: The process whereby compounds or substances in a heterogeneous solution are separated by the difference in their rates of diffusion through a semi-permeable membrane. For example, if a solution of sodium chloride and albumin is placed inside a dialysis bag immersed in water: the sodium chloride ions will diffuse outward about twenty times faster than the albumin. Thus, after a short time, the solution inside the dialysis bag will be mostly proteins.
diatom: A form of marine algae living within a tiny: silicon-containing cell. Diatoms produce huge amounts of organic materials by carrying on photosynthesis with the brown pigment fucoxanthin.
diatomic molecule: a molecule that consists of two atoms, e.g. HCl and O2 .
dichlorodifluoromethane CCl2F2: a compound, also known as Freon 12, which is the primary CFC that has been linked to the greenhouse effect. Even though the compound is found in very small concentrations, its properties make it a significant factor in stratospheric chemistry. CCl2F2 absorbs UV light in the upper stratosphere where it arrives decades after being released in the troposphere. CFCs, which were originally created by Dupont corporation, were used as refrigerants for everything from air conditioning to home refrigerators because they are non-toxic and extremely unreactive (in the troposphere). It is this unreactivity that makes them such a problem for the atmosphere, because they are able to last long enough to make it to the stratosphere, where they cause so many problems. CCl2F2 production, along with all CFCs, has been banned since the mid 1990s, but some scientists believe that the damage has already been done.
dichoric: Having the absorbency depend on the relative orientation of the pane of polarisation of incident light and a molecular axis.
dicotyledon: Any flowering plant having two cotyledons.
dictyosome: A stack of membranous vesicles similar to the Golgi complex and found in certain animal and higher plant cells. The function of dictyosomes is uncertain: but at least in plants it appears to be related to synthesis of polysaccharides.
dielectric: A substance that acts as an electrical insulator and can sustain an electric field. When a voltage is applied across a perfect dielectric there is no energy loss and the electric field changes simultaneously with voltage. In the real dielectrics: such as air: ceramics: or wax: which were used in capacitors: there is always a small energy loss.
differential fertility: A measure of the success of an inherited variation in terms of its effects on the reproductive capacities of an organism. A variation that increases reproductive capacity is considered a successful one.
differentiation: The structural or functional changes that occur in cells during the embryonic development of an organism.
diffraction: The spreading or bending of light waves as they pass the edge of an object or pass through an aperture. The diffracted waves subsequently interfere with each other producing regions of alternately high and low intensity. The phenomenon can be observed in the irregular boundary of a shadow of an object cast on a screen by a small light source. A similar effect occurs with sound waves.
diffused lighting:
digestion: The enzymatic breakdown of food from large molecules into small ones capable of entering the blood stream: and eventually the cells: by a process of absorption. Important organs of the digestive system include the stomach: pancreas: gall bladder and small intestine.
digitalis: Common foxglove and source of cardiac glycosides.
digital camera: these record images electronically. The resolution (sharpness) varies and low resolution is not suitable for some forensic applications such as fingerprints, and scene of crime shots where details may be important. They are becoming cheaper and better and it is possible that they may soon be widely used in all applications although they are more widely open to abuse than standard photographic techniques. Advantages; Rapid development (transfer to computer) Easy to e-mail, No chain of custody. All members of an investigative team may access the photos via a network. Disadvantages; Readily open to abuse as images can be easily altered.
Dillie - Koppanyi test: A chemical test for barbiturates in which the reactant turns violet - blue.
dimethyl sulphide: released by bacteria on the continents and in the oceans. Oxidized in the marine atmosphere to partially form cloud condensation nuclei and this may effect the formation of clouds over the oceans.
dimorphic (botany): Flowers that appear in two forms.
dinitrogen pentoxide: A compound that contributes to ozone depletion during springtime in the Antarctic. This occurs because ozone converts some nitrogen dioxide radical to nitrogen trioxide radical, which combines with other dinitrogen radicals to produce dinitrogen pentoxide. The reaction is reversible except in the presents of stratospheric liquid droplets where nitric acid occurs. This reaction ties up the nitrogen dioxide radical allowing more chlorine atoms to be present in the active form.
dioecious: When the staminate and pistillate flowers are borne by different plants of a species.
dioxins: a family of 75 different toxic chlorinated hydrocarbons formed as by-products in chemical reactions involving chlorine and hydrocarbons, usually at high temperatures.
diploid: term applied to a cell that contains a pair of each type of chromosome. The number of chromosomes usually given for an organism is the diploid number; hence the human has 46 chromosomes (23 pairs).
dipole: a partial positive and equal partial negative charge separated by a distance.
direct lighting :
direct reflective lighting:
discriminating power (DP) :the potential power of a system to distinguish between individuals at a locus.
dissolution: The transfer of gas to the surface of a water droplet from the bulk atmosphere: and the gas mixing within the droplet.
distillation: the separation of a mixture: making use of the fact that it's components have different boiling points.
diurnal ozone concentration: the ozone concentration in the troposphere is directly related to the pollutants that are in the air and the time of day. For example, during the early hours of the day many pollutants are released into the air. As the day progresses, the sun becomes more overhead and the concentration of the sunlight increases. This solar radiation causes chemical reactions to occur and the primary pollutants decrease while the concentration of ozone increases. Eventually the ozone breaks back down and the process is ready to proceed the next day divergence, going apart. Upper-level divergence leads to rising air. Surface divergence is associated with subsidence and high surface pressure.
divergent speciation: Evolutionary process in which single ancestral species give rise to two or more independent species.
DNA: deoxyribonucleic acid
DNA fingerprinting: restriction fragment length polymorphism
Dobson units: Measurement unit for determining the total amount of ozone present in a vertical column of air above the surface of the earth. An air layer at atmospheric pressure of 1013 hPa and temperature of 298 K which measures 1 mm in thickness and is equivalent to 100 Dobson units.
doldrums: calm, light winds, or squalls lying along the length of the equator. Winds which are part of the general circulation of the atmosphere, which are driven by the input of solar energy and modified by the rotation of the Earth. It is here that 17th and 18th century sailing ships had the most trouble making way and lack of fresh water or food sometimes spelled disaster.
dominance hierarchies: "Pecking orders" in animals in which social hierarchies serve to maintain order.
dominant gene: A gene that always expresses itself over it's recessive allele in the heterozygous condition.
dominant species: A species whose life form determines the community structure of the association, or that species which has the greatest percentage cover.
Doppler effect (Doppler shift): The apparent change in the frequency of a wave caused by relative motion between the source and the observer. When the source and the observer are approaching each other, the apparent frequency of the wave increases; when one is travelling away from the other, the apparent frequency decreases. An example of the Doppler shift is the change of pitch of the sirens of an emergency vehicle when it passes you. The effect can also be observed as a shifting of the wavelength of light from a receding star towards the red end of the spectrum. In this case the effect is known as the red shift.
Doppler radar: radar that indicates radial (in- or outbound with respect to the radar) wind speed as well as precipitation echoes; coherent radar.
dot blot: a method of quantifying DNA.
double helix: the name for the characteristic spiralling shape of the native form of DNA when single strands are held together by complementary base pairing and twisted around each other.
drugs - misuse of (Act 1971): The act of parliament in Britain that classified drugs into classes, these include: Class A. morphine, cocaine, heroin Class B. cannabis, amphetamines Class C. methaqualone.
Duquenois - Levine test: A three part reagent which finally shows purple when added to marijuana.
dry adiabatic lapse rate: rate at which unsaturated air cools as it travels vertically, provided that all temperature change is adiabatic (without heat exchange), and no condensation occurs. In dry air it can be approximated as 1 degree Celsius per 100 meters of rise. It can be used as a basis of comparison for actual temperature profiles of air and can help predict smoke stack gas dispersion characteristics.
dry bulb temperature: the actual air temperature as measured by a sling psychrometer.
dry deposition: the transfer of trace species (gases or particles) from the atmosphere to surfaces as a consequence of molecular diffusion: Brownian diffusion, or gravitation settling, in the absence of active precipitation. The term refers to the transfer process and not to the surface themselves, which may be moist.
dust: solid particles generated by mechanical action, present as airborne contaminant.
dynamic equilibrium: A state in which the concentration of reactants and products in a chemical reaction remains constant, though not necessarily in equal quantities over time.
dynamite: An explosive plastic solid consisting of 75 % nitro-glycerine and 25% kieselguhr, a porous form of silicon dioxide (SiO2). Nitro-glycerine on its own is very sensitive to shock and the kieselguhr makes it safe to handle. Dynamite is used for blasting, particularly under water.


Earth (the) : the third planet out from the Sun in the Solar System. Earth is the largest of the four terrestrial planets, with a diameter of 12, 756 km. It orbits the Sun at an average distance of 149,597,870 km ( 1 astronomical unit), and it rotates once on it's axis every 23 hours 65 minutes and 4 seconds. This is the sidereal day, measured relative to the distant stars; because of the movement of the Earth in its orbit as it rotates, the time from noon one day to noon the next day (the solar day) is a little longer - 24 hours, or 86, 400 seconds. It takes 365. 24 solar days (1 year) for the Earth to travel once around its orbit, from equinox to equinox. The atmosphere of the Earth is intermediate in density between those of Venus and Mars, its nearest planetary neighbours, and the planet is unique among those of the Solar System in having large oceans of liquid water. The atmosphere today consists of 77% nitrogen, 21% oxygen, 1% water vapour, 0.9% argon and traces of other gasses, the most important oh which is carbon dioxide (see Greenhouse effect). Earth is the only planet known to be geologically active, and has a surface which is only very young in geological terms, having been produced by the processes of plate tectonics. These destroy old crust by pushing it below the Earth's surface in deep ocean trenches, while making new crust from molten material spewed out by volcanic activity at the sites of spreading ridges in the oceans. As well as being geologically young, the surface of the Earth is constantly being changed by erosion caused by wind, water and waves, and by biological activity. This makes it difficult to pick out surface features corresponding to the craters of the Moon, Mars, and Mercury (and revealed by radar mapping on Venus), but geological evidence shows that, like the other terrestrial planets, Earth was subjected to intense meteoritic bombardment early in its life. The mass of the Earth is 5.976 x 1027 grams, and its volume is 1.083 x 1027 cubic cm, so that its overall density is just over 5.5g/cubic cm, five and a half times that of water. The solid crust of the Earth is only 5 km thick under the oceans, and averages about 30 km thickness on the continents. Beneath its skin, a region known as the mantle, subdivided into different layers, extends down to within 5,000 km of the centre of the planet, which is an iron-rich core. The mantle makes up 82% of the Earth's volume, and it is thought to be made of silicate rocks. The solid inner core, with a radius of 1,700 km, is divided from the mantle by a semiliquid outer core; the temperature in the core is about 3000 Kelvin. The density rises from about 13.5 times that of water in the core to between 5.5 and 3.5 times the density of water in the mantle, and averages about 3 times the density of water in the rocks of the crust. The Earth is at aphelion on the 3rd July each year. echo, the energy received on radar which results from back-scattered energy; indicates the presence of precipitation (targets). ecliptic, The great circle in which the plane of the earth's orbit around the sun meets the celestial sphere. As a result of the earth's orbital motion, the ecliptic marks the apparent path of the sun across the celestial sphere, relative to the background stars, over the course of a year.
ecliptic : The plane of orbit of the earth around the sun.
ecology : Branch of biology which focuses on the relationships among various species and among the species and their environments. The basic units for study are the species (all the organisms which are capable of interbreeding), population (all of the members of a species occupying a certain geographical area) and community (number of populations interacting within a certain area). The emphasis in environmental science, however, is on the processes of energy flows and nutrient cycles within these communities and ecosystems and involves such ideas as species abundance, biodiversity, complexity, trophic (feeding status) levels, ecological niches, and structure of communities.
ecology : The study of the relationship between plants and animals, and their environment.
ecosystem : all the interacting factors, both physical and biological, forming a biotic community.
ectodactyly: where one or more digits have been absent since birth.
ecotoxicology : the study of toxic effects of chemical and physical agents on living organisms as well as human beings, especially on populations and communities within defined ecosystems.
ectoderm : In an embryo, the outer germ layer giving rise to the epidermis, the neural tube, and the epithelial lining of the vertebrae.
eddy diffusion : the exchange of gaseous components of the atmosphere in a turbulent flow by rapid mixing of fluid eddies.
efflorescence : the reverse process of deliquescence; the drying of a salt solution when the vapor pressure of the saturated solution of a substance is greater than that of the ambient air.
effusion : The movement of gas molecules through an opening that has relatively large holes.
electrochemical cell : two electrodes in electrical contact with each other and with solution (the electrolyte).
electrode : an experimental arrangement (normally involving a metal conductor) at which oxidation or reduction occurs in an electrochemical cell.
electromagnetic radiation : Transverse waves consisting of electric and magnetic fields vibrating perpendicularly to each other and to the direction of propagation. In free space the waves are propagated at a velocity of 2.9979 x 108 metres per second, known as the velocity of light (c). Their wavelength (l) and frequency (f), are related by the equation lf = c . Those with the highest frequencies are known as gamma radiation; then in descending order of frequency the electromagnetic spectrum includes X-rays, ultraviolet radiation, visible light, infra-red radiation, microwaves and radio-waves.

electromagnetic units (emu) : a system of electrical units based on the unit magnet pole, which repels a similar pole one centimetre away with a force of one dyne. Electromagnetic units have the prefix attached to the practical unit (e.g. abvolt).
electromotive force (emf) : The electrical potential difference or potential voltage between two points in an electric circuit. It causes the movement of charge that constitutes an electric current, providing a limited analogy to mechanical force and motion.
electron : a negatively charged sub-atomic particle.
electron capture detector : one of the most sensitive gas chromatographic detector for halogen-containing compounds like chlorofluorocarbons. James Lovelock's early work with this detector led to the discovery that anthropogenic chlorofluorocarbons used most heavily in the Northern hemisphere were very long-lived and therefore well-mixed throughout the troposphere. Later work by Rowland and Molina suggested that CFCs also difussed into the stratosphere where their chlorine atoms could by freed by photolysis-CFC bond breaking by UV light. The result of this is the destruction of ozone molecules in the important ozone layer of the stratosphere.
electron gain enthalpy (DH oeg ) : the standard enthalpy change when one mol of anions is formed, all species being in the gas phase.
electronegativity : the measure of the ability of an atom to attract bonding electrons to itself when it is joined to another by a covalent bond.
electrophoresis : In biochemistry, a process used to separate different kinds of organic molecules from each other in a mixture. Electrophoresis takes advantage of the differences in overall net electric charge on different kinds of molecules. When a mixture of molecules is placed on a moist surface (such as a gel) through which an electric current passes, molecules with an overall net positive charge move toward the negative pole (cathode) and those with a net negative charge move toward the positive pole (anode). Rates of migration also vary: molecules with more negative charges migrate toward the positive pole more rapidly than those with a less negative charge, etc. In this way different types of molecules tend to separate out together at different regions along the gel or other surface.
electrostatic precipitator : a device that reduces pollution from smokestacks. It gives the particles in smoke a electrical charge. The charged particles are then collected on filters that have the opposite charge and thereby removed from the emission stream.
electrovalent (ionic) bond : Where an outer electron is transferred from one atom to another so that ions are formed. The electrostatic force between the ions hold the molecule or crystal together. For example, a molecule of sodium chloride (NaCl) is formed when the single electron in the outer shell of the sodium atom is transferred to the chlorine atom. As the chlorine atom has seven electrons it gives it the eight electron argon stability.
element : a substance in which all the atoms have the same atomic number. Matter that can not be broken down into anything simpler by chemical reactions.
elementary reaction : an individual reaction step; part of an overall reaction mechanism.
El Nino : A condition caused by the decrease in atmospheric pressure over the Eastern Pacific Ocean, weakening the prevailing westerly winds and resulting in warm waters and less nutrient replacement from cold, deeper waters into the Eastern Pacific along the coast of South America. El Nino creates strange weather patterns worldwide sometimes causing flooding in California and droughts in South America simultaneously. The effect gets it name from the Spanish for the Christ Child--the little one--because it is experienced in December by the local fisherman off the western coast of South America as a poor fishing season.
El Nino-Southern Oscillation (ENSO) : the relationship of the El Nino conditions and the Southern Oscillation pattern (The Walker Circulation). A high pressure over the Pacific Ocean and low pressure over the East Indies causes heavy rainfall across the Pacific, rise in the sea level and increased surface temperatures.
elliptic : An object having the shape of an ellipse: a squashed or elongated circle. The sun follows an elliptic path across the sky.
elution : The process of removing material from a chromatographic system.
embryology : The study of the structural and functional development of an organism during it's early life.
embryonic induction : The ability of one type of embryonic germ layer to trigger or specifically influence the differentiation of another germ layer (which usually has direct contact with it).
embryonic region : The growth region in roots, located just behind the root cap, where new cells are produced by rapid cell division.
emission (of light) : the giving out of a photon of light by an atom, molecule or ion.
emission : The release or giving out of a gas, light or heat. An automobile releases uncombusted or partially oxidized hydrocarbon emissions from its tailpipe when the engine is running. Atoms in an excited state often emit light in order to reach a lower energy state. These emissions can be used to determine the presence of the atoms in a sample.
empirical formula : a chemical formula that uses the smallest whole number ratio of the atoms present in a compound.
emulsifying agent : a substance that stabilises an emulsion so allowing emulsification.
emulsion : a colloidal solution consisting of one liquid dispersed in another.
endergonic : Term applied to those chemical reactions that result in an overall increase in energy among the formed products and hence the storage of energy. Photosynthesis is an endergonic reaction.
endocrine system : The system that contains all of the hormone secreting glands in the body. endoderm, In an animal embryo, the inner-most germ layer, which gives rise to the lining of the gut.
endonuclease : An enzyme that makes internal phosphodiester cuts in the sugar-phosphate chain of polynucleotide.
endoplasmic reticulum : a maze of membranes in the cytoplasm, at places continuous with the nuclear envelope. The endoplasmic reticulum may serve to increase the surface area of the cell and thus aid in exchange of material.
endothermic : any chemical reaction in which heat is absorbed from the surrounding environment.
end point : in a titration, the point at which enough solution has been added so that the indicator begins to change colour. Ideally, the end point should equal the equivalence point.
energy barrier : The amount of energy that any non-excited atom or molecule must gain in order to become "excited" and enter into a chemical reaction.
enhanced greenhouse effect : Increasing the concentration of the trace gases in the air that absorb thermal infrared light, i.e. greenhouse gases, will result in more infrared light redirected to the earth causing an increase in temperatures.
enthalpy (H) : a thermodynamic variable that is a system's internal energy plus the product of its pressure and volume: H = E + PV.
enthalpy of fusion : the standard enthalpy change when 1g (or 1 mol) of a liquid is formed from 1g (or 1 mol) of solid without a change in temperature; units are J g-1 or J mol-1.
enthalpy of vapourisation : The amount of heat required to convert 1 gram of a liquid at boiling point to 1 gram of gas; units are J g-1 or J mol-1.
entrainment : the act of air being drawn into a cloud from the non-cloud environment.
environmental gradient concept : The model that states that plant's requirements are responsible for their positioning (every plant having an optimum area within each of the ecological gradients).
environmental resistance : Factors in the environment that oppose or limit the increase in numbers of a given population.
enzyme : A protein, the synthesis of which is controlled and directed by a specific gene. Enzymes act as catalysts, directing all major chemical reactions in the living organism.
Eocene epoch : Second epoch of the Tertiary period lasting from about 54.9 to 38 million years ago. This was a period of rising global temperatures.
epidemiology : the study in populations of health factors affecting the occurrence and resolution of disease and other health-related conditions.
epididymis : A single, complexly coiled tube lying on top of the mammalian testes in which sperm is stored.
epigenesis : In embryology, the idea that an entire organism develops from an originally undifferentiated mass of living material.
epiphyles : Plants which grow on others to obtain better support but not able to obtain nourishment from them.
epithelium : One or more layers of cells united together by an interstitial cement-substance, supported on a basement membrane. Naturally grouped into two classes , according as to whether there is a single layer of cells (simple epithelium) or a multiple layer (stratified epithelium). The different varieties include; squamous, columnar, glandular or spheroid and cilated.
epsilon ( E, e ):
Equatorial rain forests : An area located near the equator worldwide, covering seven percent of the earth's surface, characterized by high precipitation, absent or short dry season, high tree and vegetative growth rates, high humidity, high photosynthetic rates and extreme biodiversity. The equatorial rain forests produce much of the oxygen in the Earth's atmosphere and absorbs large quantities of carbon dioxide from the air. (See deforestation.)
equilibrium : a dynamic equilibrium is a state of balance that is produced by two opposing processes (e.g. forward and back reactions) which are occurring at the same rate.
equilibrium composition : a particular set of concentrations of reactants and products at equilibrium.
equilibrium-constant expressions : These are algebraic equations that describe the concentration relationships that exist among reactants and products at equilibrium. Among other things, equilibrium-constant expressions permit calculation of the error resulting from the quantity of unreacted analyte that remains when a steady state has be reached.
equilibrium constant (Kc) : a ratio (defined by the reaction equation) involving the concentrations of reactants in an equilibrium.
equilibrium phase : The stage where growth rate in a population of cells or organisms has levelled off, so that the appearance of new cells or organisms just equals the disappearance of old ones.
equinox : Either of the two points at which the ecliptic intersects the celestial equator. The ecliptic represents the apparent annual path of the Sun around the celestial sphere. The sun crosses the celestial equator from S to N at the vernal equinox, usually on March 21st. It crosses from N to S at the autumnal equinox, usually on Sept. 23rd. At the equinoxes the centre of the sun is above and below he horizon for equal lengths of time and night and day are of almost equal duration.
equinox : Twice during the year, September 21 and March 21, the length of day and night are equal because the tilt of the Earth's axis (in relationship to the sun) is nullified and both the Northern and Southern Hemispheres receive equal quantities of sunlight.
erg : Unit of energy equivalent to the work done when a force of one dyne acts through a distance of one cm. 1 erg = 10-7 joule.
ergot : A disease caused by the parasitic fungus Claviceps purpurea which affects cereals and grasses, especially rye.
ergotamine : A drug found in ergot and closely related to LSD.
erythema :reddening of skin, inflammation.
erythrocyte : Red blood cells. Erythrocytes contain haemoglobin (hence their red colour) and serve as oxygen carriers.
ester bond : The anhydrous bond in lipids formed by removing a hydroxide from the carboxyl group of a fatty acid and a hydrogen from an alcohol group of glycerol.
estrous cycle : The recurrent, restricted periods of sexual receptivity in the non-human mammalian female, marked not only by egg production but also by increased sexual drive.
eta ( H, h ) :
ethane : A hydrocarbon found in the atmosphere whose primary fate is to react with free radicals such as chlorine and nitrous oxide. This reaction would prevent these radicals from reacting with ozone which is needed in the stratosphere to block ultraviolet light from reaching the surface of the earth.
ethanol : Also known as ethyl alcohol or alcohol, (C2H5OH) is an oxygenated hydrocarbon that can be burned as a fuel, or blended into gasoline. Thought of as an alternative fuel and clean fuel, ethanol is a renewable energy source that is made from corn or other grains. If blended into gasoline, ethanol helps with the combustion process and therefore less unburned hydrocarbons form. Ethanol blended fuels competed with methyltertbutylether (MTBE), but because of the cost and the fact MTBE can be shipped through exisisting pipelines, MTBE was chosen. MTBE is now being banned because of its ability to travel in ground water and the bad taste it imparts to drinking water, because of this ethanol is once again being put back into the gas.
ethology : The study of animal behaviour.
eukaryotes : Cells characterised by true nuclei bounded by a nuclear membrane. The cells of all protozoa and higher animals, most algae (except blue-greens) and higher plants are eukaryotes, i.e. they are eucaryotic.
eugenics : The attempt to improve the human genetic stock by encouraging breeding of those presumed to have "desirable" genes (positive eugenics) and discouraging breeding of those presumed to have "undesirable" genes (negative eugenics).
euglena : A single celled organism living in water and taking food like an animal, but also contains chlorophyll and is therefore able to manufacture food in the same way as a plant Eustatic Changes - A consistent change in the sea level that affect oceans, throughout the world.
eutrophication : The successional process leading from an aquatic system with low productivity through increasingly greater productivity to the ultimate development of a terrestrial system on the same site.
evaporation : the change of state from liquid water to vapour, requires energy (latent heat is absorbed).
evaporation : The process of the change in the state of a liquid or solid to a gas or vapor. Vanishing of the surface of a liquid to the atmosphere.
evapotranspiration : The total water loss due to the transpiration of vegetation plus the evaporation from the soil; higher climatic temperatures result in a higher evapotranspiration rate.
evolution of life on earth :
Years ago
( x 109 )
  • oldest known rocks formed
  • amino acids
  • biogenesis of anaerobes
  • oldest fossils (Stromatolites)
  • prokaryotes develop
  • photosynthesis
  • ferric iron
  • eukaryotes
  • O2 1% atmosphere
  • ozone layer from ultra violet reaction
  • Oceans pH and salinity at today's levels
  • O2 levels increasing/ CO2 levels decreasing
  • Algae and most animal pryla
0.44 colonisation of land by plants and animals fish, insects and amphibians.
0.34forests reptiles and insects increase
0.24 dinosaurs and mammals present
0.14 flowering plants and birds present
0.07pollinating insects evolve
0.002people appear.

exa (E): 1018
excretion : The removal of the waste products of metabolic activity. In higher organisms, the blood bathes each cell and carries away waste. The waste material is removed from the blood by the kidneys, the sweat glands and the lungs.
exergonic : Term applied to those chemical reactions in which the end products have less energy than the reactants. Exergonic reactions give off energy. Respiration is an example of an exergonic reaction.
exon : the portion of a DNA sequence in a gene that contains the codons which code for a protein product (after the intervening , non-coding sequences (introns) have been spliced out) as well as the beginning and end of a coding sequence.
exoneuclease : An enzyme that cuts of nucleotides one by one from the end of a polynucleotide strand by breaking phosphodiester bonds.
exothermic : a reaction in which energy, or heat of the product is released into the surroundings during the reaction.
experimental group : In an experiment, the objects or organisms whose environment is altered so that their resulting responses may be studied.
explosives : Substances that can be made to produce a large volume of gas very suddenly. The energy of he expanding gasses may be used for a number of industrial or military purposes. There are three main types. Mechanical explosives depend on a physical reaction, such as overloading a container of gas until it bursts. They are little used except in specialised mining applications where the release of chemicals is undesirable. In nuclear explosions a chain reaction takes place in a sudden uncontrolled manner, releasing energy almost instantaneously. This is used for bombs and occasionally for mining. Most explosives used are chemical explosives. These include TNT, nitro-glycerine, dynamite, and water gels, which are plastic, water resistant, and easy to handle safely.
exposure (photopraphy) : Aperture priority: the photographer fixes the aperture and the camera selects the shutter speed. Shutter priority: the photographer fixes the shutter speed and the camera selects the aperture. Program: a combination to obtain the maximum depth of field (small aperture) without camera shake (long exposure).
extinct : No longer present in the world population of organisms.
extinction coefficient : A measure of the rate of the reduction of transmitted light through a substance.
extrapolation : The calculation of values or prediction of an event beyond a given series of values or events, based on observing the trend up to a certain point.
extremophiles : Organisms which live optimally at extreme conditions (generally bacteria -prokaryotic cells).


F- actin : Polymeric form of actin.
Fabry's disease : A hereditary disease that produces high levels of sphingolipid.
facilitated transport : The movement of substances across a cell membrane from an area of higher concentration to one of lower concentration more rapidly than would occur by simple diffusion, but without the expenditure of energy.
fallopian tubes : In humans and other mammals, the name for the oviduct, a connecting passageway by which the ova (eggs) from the ovary are carried to the uterus.
farad (F) : The SI unit of capacitance equal to the capacitance of a parallel plate capacitor with a potential difference of one volt across its plates when the capacitor is charged with one coulomb.
Faraday constant (F) : a constant which is equivalent to 96.487joules per mole per volt.
Faraday's laws of electrolysis :
1. The mass of a substance produced by an electrolytic reaction varies directly with the amount of electricity passed through the cell.
2. The masses of substances produced by a given amount of electricity are proportional to the equivalent masses of the substances.
fateful species :species only found in that particular community. Whilst they may not be omni-present they will not be found elsewhere.
fats : Lipid compounds composed of glycerol and fatty acids. Fats are energy rich compounds, often stored in adipose (fat) tissue.
fatty acid : Organic molecule commodes of a long hydrocarbon chain and terminal acid (carboxyl) group.
fauna : Animals or animal life of a particular region or a particular time.
feedback cycle : the increase of the input into a system, which produces a negative or a positive output in a system of interlocking components; the return of a part or the effects of the output to the input. A proposed positive feedback cycle involves the outgassing of carbon dioxide from the planet's oceans: Since CO2 solubility in water DECREASES with temperature and since CO2 is a greenhouse gas, a positive (and possibly runaway) feedback cycle might involve the following: increased greenhouse warming of the atmosphere by IR absorbing CO2 in the gas phase, and the subsequent heating of the oceans, could increase the amount of carbon dioxide released into the atmosphere from the oceans. This might thereby increase greenhouse warming, which would, in turn, again heat the atmosphere and the ocean, etc. Though the process is no doubt more complicated than this, a runaway greenhouse effect is usually given as the reason for Venus' high surface temperatures.
feedback mechanism : A self regulating mechanism within all homeostatic systems. Part of the out put of the system is cycled back into the system itself in order to regulate further function and out put.
femto (f) : 10-15
ferredoxin : An iron rich protein found in photosynthetic organisms. During the light reaction, this compound is capable of accepting free electrons and passing them through a reducing system to generate reduced NADP ( that is, NADPH) and ATP.
ferredoxin-reducing substance (FRS) : Hypothesised primary electron acceptor after light absorption by chlorophyll. FRS passes electrons from chlorophyll to ferredoxin.
ferritin : An iron containing protein used as a marker in electron microscopy.
fertilisation : In sexual reproduction, the union of the male(sperm) and the female (ovum) gametes to form a diploid cell (the zygote) capable of developing into a new organism.
fertilisation membrane : A protective membrane that surrounds the egg once it has been fertilised by a single sperm and thus prevents multiple fertilisation's.
fertilizin : A carbohydrate and protein substance produced by the egg, capable of causing the agglutination of sperm or the binding of the sperm to the egg.
fibrin : A long protein polymer composing the fibrous part of blood clots. Fibrin is produced from the soluble blood protein fibrinogen by the action of the enzyme thrombin. filament (botany), the stalk like portion of the stamen.
fire : There are five main classifications for fire, these are:
Class A; Wood, paper, fabric,
Class B; Hydrocarbons,
Class C; Electrical systems and equipment,
Class D; Combustible metals,
Class E; Radio-active materials.
fireball : A meteor which is brighter than any planet or star, i.e. brighter than magnitude -4.
fire extinguisher :
fire point : The minimum temperature at which a mixture of gas/vapor and air continues to burn in an open container when ignited. The value is generally above the flash point.
firn : Granular snow that has endured a summer without melting and will transform into glacial ice.
first law of thermodynamics : A physical principle which states that matter is neither lost nor gained during ordinary chemical reactions. This law may more accurately be described as the law of conservation of matter and energy: the sum total of matter and energy in the universe remains constant.
fission : A rapid and efficient method of reproduction, found in many micro-organisms, which involves splitting by mitosis and cell division of one cell into two, each of which is genetically identical to the other.
fixed focus : A lens with a short focal length and a small lens opening will have a large depth of field. No focussing is required unless a subject is very close.
flagellum (pl. flagella) : A long whip-like extension of cytoplasm from unicellular organisms such as Chlaydomonas, or most animal sperm. An outer membrane encloses a highly structured matrix which surrounds microtubules arranged in the familiar 9+2 pattern found also in cilia (a 9 + 0 arrangement is found in centrioles). The function of flagella is movement of the cell.
flame analysis : The observational tool used to roughly determine the materials involved in a fire :

MaterialFlame colourSmoke colour
benzeneyellow/white grey/white
cloth yellow/redgrey/brown
cooking oilyellowbrown
lacquer thinnersyellow/redgrey/brown
lubricating oilyellow/whitegrey/brown
naphtha oilstraw/whitebrown/black
paper yellow/redgrey/brown
wood yellow/redgrey/brown

flammable range : The concentrations of flammable gas or vapor between the LEL and UEL at a given temperature.
flash point :The lowest temperature required to raise the vapor pressure of a liquid such that vapor concentration in air near the surface of the liquid is within the flammable range, and as such the air/vapor mixture will ignite in the presence of a suitable ignition source, usually a flame. (Open cup values are approximately 5.5oC to 8.3oC higher than the closed cup values).
fledge : The acquisition, by a nestling, of feathers enabling flight.
flora : a plant or plant life of a specific region or particular period.
flux : The rate of continuous change, flow or movement of liquid, particles or energy. The rate of discharge of a liquid, removal of energy or particle depositing from one body to another.
f number :
focal length :
foehn : A warm, dry wind on the lee side of a mountain range that owes its relatively high temperatures largely to adiabatic heating during descent down mountain slopes. In Zurich Switzerland, this means a warm but clear view of the Alps.
fog (mists) : Liquid aerosols formed either by condensation of a liquid on particulate nodes in air or by uptake of liquid by hygroscopic particles.
follicle (botany) : A dry one-celled and one valved fruit, containing more than one seed.
follicle stimulating hormone (FSH) : A goadotropin, one of the hormones secreted by the anterior pituitary gland which in mammalian females stimulates the growth of ovarian follicles into oestrogen-secreting glands (i.e., corpus luteum). In males FSH stimulates spermatogenesis.
food chain : The transfer of energy from one organism to another, starting with the primary producers (photosynthetic organisms), or through primary consumers (herbivores), secondary consumers (carnivores), and decomposers (detritivores). food web : A complex set of interactions within an ecosystem in which any given species usually serves as both prey and predator. All living forms in the ecosystem have a variety of functions. Thus there is no single one-way street of food consumption hierarchies.
foramen ovale : An opening in the foetal heart allowing blood to pass directly from the right to the left atrium, by passing the pulmonary transit.
formaldehyde - CH2O : A colorless, pungent, carcinogenic, and toxic gas which can irritate membranes. It is used as formalin in its aqueous state (37 %). formaldehyde is reactive due to its carbonyl functional group.
formic acid - CH2O2 : A weak acid that photolytically reacts in the atmosphere forming COOH radical and H radical. This compound often reacts with the hydroxyl radical and atomic oxygen to form formic acid and a hydroperoxy radical. This is a sink for the hydroxyl radical and it also helps drive other reactions with the addition of hydroperoxy radicals to the atmosphere.
fossil fuels : There are coal, crude oils, oil shales, tar sands and natural gases such as butane, ethane, methane which occur naturally from the decomposition of plant and sea and land organisms over millions of years. These natural resources contain stored energy from the sun which is released upon combustion. These fuels also release various types of pollutants such as sulfur dioxide, carbon dioxide and nitrogen dioxide when burned.
fractional distillation :
free radicals : highly reactive atoms or molecules with incomplete (electronic) octets and therefore uneven numbers of electrons. (In the case of hydrogen radical this is an incomplete duet.) Free radicals species are very electrophilic, will abstract atoms from other molecules to complete their octets, and will, in the process, generate new radicals. In the atmosphere, most free radical species have short life times; however, they can promote the conversion of oxygen to ozone and also take part in the catalytic cycle of ozone destruction (see chlorine and chlorine monoxide freezing rain, rain that falls as liquid water but freezes on contact with a cold surface.
freons (also see CFCs): Stable liquids or gases usually produced for solvents, aerosol propellants, refrigeration, air conditioner or styrofoam purposes. These high vapor pressure liquids/gases are chemically stable and have long atmospheric lifetimes; therefore, they can eventually become well-mixed in the troposphere and ultimately diffuse into the stratosphere. Upon encountering high energy UV light in the upper stratosphere these species are photodissociated and ultimately release all of their atoms there. The free radical chlorines (or bromines in the case of some halons) catalytically destroy ozone (see chlorine) in the stratosphere.
frequency : The number of cycles completed by a vibrating system in unit time, usually one second (symbol: v or f). The unit of frequency is the hertz. The angular frequency, w, is related to the frequency by the equation w = 2pf, and is measured in radians per second.
front : a narrow transition zone between two different air masses. Important mechanism for lifting air. A convergent boundary. A front is synoptic scale along the length of the front, but mesoscale across the front itself.
frontal wedging : the lifting of air resulting when cool air acts as a barrier over which warmer, lighter air will rise.
fructose : A simple sugar (monosaccharide) that is sweeter than sucrose and present in green leaves, fruits and honey. Its phosphate derivatives are important tin the carbohydrate metabolism of living organisms. It is a keto hexose sugar.
fruit : The fertilised and mature ovary or carpel.
Fujita (F) scale : the scale used to measure the severity of tornadoes. The value on the scale is determined by the amount of damage caused.
click here to see scale
fumes : airborne solid particles that have condensed from the vapor state.
fungi : Any of a large group of non-flowering plants including mushrooms, toadstools, moulds and yeast.
furrowing : The infolding of the cell membrane by an animal cell during telophase.


Gaia Hypothesis : an hypothesis proposed during the early 1970s by James Lovelock which states that all living organisms have the ability to affect their surroundings such as the atmosphere, lithosphere, and climate to maximize its biological success. The hypothesis connects the evolution and survival of a species to the evolution and conditions of its environment.
gametes : male or female reproductive cells containing half the total number of chromosomes (that is, the haploid number) for any given species. These germ cells are formed by the process of meiosis (reduction division) from diploid cells.
gametiphyte : The small, photosynthetic, haploid stage in the life cycle of lower plants such as mosses and ferns. The gametiphyte contains male and female gamete producing organs.
gamma (G, g):
gamma radiation : Highly energetic electromagnetic radiation emitted by certain radioactive substances, as a result of transactions of nucleons from a higher to a lower energy level and when an elementary particle and its anti particle annihilate each other. The wavelength of gamma radiation is between 10-10 and 10-14 metre.
gas constant (R): The constant that appears in the ideal gas law: pV = RT. Its value is 8.314 joules per Kelvin per mole.
gastrula : The embryonic stage produced by gastrulation. A hollow structure generated by infolding of the blastula and consisting of two germ layers.
Gaucher's disease : An autosomal recessive with a gene frequently approaching 0.01 in some Jewish populations, is a defect in the hydrolysis of the G1c-ceramide bond that occurs in both gangliosides and globosides. Gaucher's disease affects many tissues, but the accumulation of glucosylceramide is especially conspicuous in the spleen and liver, which are enlarged owing to the turnover of the globoside-rich erythrocytes and leukocytes.
Gause's hypothesis : The principle of competitive exclusion which states that two species with similar ecological requirements cannot successfully live together for any length of time because of their competition for all the basic requirements of life.
gauss :
Electromagnetic unit of magnetic induction.
Geiger counter : A device that detects and counts ionising radiation and particles. Essentially it consists of a metal cylinder containing low pressure gas and a wire anode running along it's central axis. The anode is held at potential difference at just less than that required to produce a discharge of the gas. Ionizing particles passing into the tube through a window at one end induce discharges, which can be counted by a suitable current.
gegenschein : A very faint glow in the night sky that can sometimes be seen on the ecliptic in a direction directly opposite the sun's position. It is part of the zodiacal light.
gel electrophoresis : Separation of electrically charged molecules in a solution by passing them through a solid medium under the influence of an electric field.
gelignite : A high explosive consisting of nitro-glycerine, cellulose nitrate, potassium nitrate and wood pulp.
gelsemium :
gene : A part of the hereditary material located on a chromosome. The term "gene" was first used by Johannsen to mean something in a gamete which determined some characteristic of an adult. The gene concept has been refined to the idea of a single gene as the source of information for the synthesis of a single polypeptide.
gene pool : The total genetic make up of a particular population, consisting of all the alleles existing in that population at any given time, regardless of their proportions. This concept provides a way of looking at the possible genetic changes that may occur in a freely breeding population from one generation to another. If 100 organisms (composing a hypothetical population) have 10 genes each (with 2 alleles for each gene) then the gene pool for that population consists of 2000 genes.
general circulation models : Three dimensional computer simulations of climate and weather which, through calculations, are used to investigate gravity wave fields. The models may help to predict atmospheric chemistry distribution and meteorological trends for the future.
general relativity theory :
genetic code : The linear sequence of bases along a DNA molecule which in turn determines the sequence of amino acids in a polypeptide chain. The code itself consists of triplet groups, each specific three bases coding one amino acid. It has been found that more than one triplet can code for the same amino acid; thus the term "degenerate" is used in reference to the genetic code.
genetic drift : A condition in which one allele becomes fixed in a population. Genetic drift is a major factor only in a very small population of organisms.
genetic equilibrium : The maintenance of a more or less constant ratio between the different alleles in a gene pool from generation to generation (often stated as the Hardy Weinberg law).
genetic map : A diagram showing the mutual locations of genes within a chromosome.
genotype : The genetic make-up of an organism; what alleles it actually contains and can pass on to its offspring.
genus (pl. genera) : The assemblage of species which all agree in one or more important structural characters.
geocentric distance (delta) : The distance of an object from Earth, usually given in astronomical units.
geochemists : Chemists who study the earth by analyzing its minerals, rocks, the crust, salts and other lithospheric properties. They use reactions such as chemical weathering, dissolution, hydration, dehydration, oxidation to explore the relationship between chemical processes and reactions with the atmosphere and hydrosphere.
geochronology :




Years Ago

geographic isolation : The physical division of an original population into geographically separate groups. Such isolation is usually followed by divergence and speciation.
geology : The study of the Earth; it's origin, history, structure, composition, and the natural processes acting on it. Branches of geology are historical (including geochronology, stratigraphy and palaentology); physical (including geomorphology, geophysics, petrology, mineralogy, crystallography and geochemistry); and economic, involving the distribution and occurrence of the economically important rocks and minerals, such as petroleum.
geostrophic wind : wind that flows parallel to the isobars in a straight line; a balance between the pressure gradient force and the Coriolis force. The pressure gradient force is balanced by the Coriolis force in the geostrophic balance.
germ plasm : The term developed to describe the productive cell which directly produce the gametes for the next generation. It was believed that the germ plasm is "immortal", i.e. it has continuity with the germ plasms of the preceding and succeeding generations through the process of sexual reproduction. Changes in somatoplasm (body cells) do not affect the germ plasm
germinal ridges : Precursors of the primordial gonads in human and most mammalian embryos. Germinal ridges develop as thickenings of the mesodermal epithelium lining the primitive coelom.
gestation period : The period required for a mammalian embryo to develop from fertilisation until birth.
ghost : Haemoglobin-free sac of an erythrocyte after the release of its contents.
giant star : a large very luminous star that has a very tenuous atmosphere but a dense core. It is in a late stage of evolution, having exhausted the normal source of energy in it's core (hydrogen), and must obtain energy from other nuclear fusion reactions. This causes it's size and temperature to alter as it evolves.
giga (G) : 109
gigayears : Time measured in billions of years; a common measure of geologic time.
gilbert (Gb) : A unit of magneto-motive force equivalent to the magneto-motive force produced by a current of 40 amperes passing through a single coil.
glaciation : The process of forming glaciers.
glacier : A slow-moving mass of ice formed in higher latitudes and elevations. When snowfall is greater than melting and the increasing amounts of snow become compacted and pressurized it forms firn and ultimately a glacier. As the glacier moves, it carries rocks and soil, and can form u-shaped valleys over geologic time. Glaciers can move at variable rates.
glands : Specialised tissues that secrete hormones.
global climate model : A computer program that is used by atmospheric scientists to study and predict world-wide trends in weather patterns and the forces and physical laws that affect climate. The formulae are complicated and require skilled mathematicians, atmospheric scientists, and powerful computers for execution. Five regimes that influence climate are often taken into consideration: atmosphere, hydrosphere, biosphere, cryosphere, and pedosphere. Atmospheric and environmental physical laws as well as principles of thermodynamics and hydrodynamics are all used as part of the extensive mathematical parameters for the program. The results of these models are used as reference for other models, policy decisions, and by meteorologists.
Global Precipitation Climatology Project : This is an element of the Global Energy and Water Cycle Experiment (GEWEX) of the World Climate Research program(WCRP). It was established by the WCRP in 1986 with the initial goal of providing monthly mean precipitation data on a 2.5 x 2.5 degree latitude-longitude grid for the period 1986-95. It was recently extended to the year 2000. The GPCP will accomplish this by merging infrared and microwave satellite estimates of precipitation with rain gauge data from more than 30,000 stations. These data sets will be used to validate general circulation and climate models, study the global hydrological cycle and diagnose the variability of the global climae system.
Global Warming : The overall increase of atmospheric temperature due to a buildup of greenhouse gases.
globin : The protein portion of haemoglobin.
glucose (dextrose) : A simple sugar (C6H12)6 and an essential substance in the carbohydrate metabolism of living organisms. Carbohydrates (such as starch and glycogen) in food or tissue reserves are broken down into glucose, which is easily transported to cells where it undergoes glycosis to provide energy for the cell. Organisms can also manufacture glucose from fats and proteins. Glucose levels in blood are regulated by the hormones insulin and glucagon and small amounts of glucose are normally present in urine. Fruits and honey are good sources of glucose.
glycoprotein : A protein to which a carbohydrate is covalently linked.
glycosis : The initial stage of respiration, involving the breakdown of glucose to pyruvic acid. In aerobic respiration, glycosis yields pyruvic acid for the citric acid cycle. In anaerobic respiration the pyruvic acid is converted to lactic acid (as in bacteria and the muscle cells of living organisms), or into ethyl alcohol (as in yeasts).
glycosidic bond : The anhydrous bonds of carbohydrates formed by removing a hydrogen from an alcohol group of one sugar and a hydroxide from an aldahyde group of the other. Glycosidic bonds hold together the sub-units (such as glucose) making up long chain polysaccharides.
Golgi apparatus :
Golgi complex (Golgi body) : A cluster of flattened, parallel smooth surface membranous sacs found within the cytoplasm. The Golgi complex appears to function in isolating, packaging, and transporting molecules out of the cell.
gonadotropins : General names for the group of hormones produced and secreted either by the pituitary gland of both sexes or by the placenta during pregnancy in the mammalian female. Gonadotropins act as a stimulator of the reproductive organs; their increased production by the pituitary at puberty is responsible, in part, for the growth of the ovaries or testes.
Gondwanaland : A hypothetical supercontinent comprising approximately the present continents of the southern hemisphere. See also Pangaea.
gout : A disease arising from the precipitation of uric acid in cartilaginous tissues.
gradient wind : wind that flows parallel to the isobars, but non-linearly. Wind that curves cyclonically is sub-geostrophic, or slower than the geostrophic approximation would predict the wind to be, while wind that curves anti-cyclonically is faster, or super-geostrophic; results from a balance among the PGF, the Coriolis force and the centrifugal force.
graffian follicles : Vesicles in the ovary in which the eggs are produced. One egg is produced per follicle. After ovulation, a follicle becomes transformed into the corpus luteum, providing progesterone which builds up the uterine lining.
grain : Unit of weight used in conjunction with pharmaceuticals and equivalent to 6.48 x 10-2 grams
grana (sing, granum) : Dense stacks of membranes that are part of the lamellar system within chloroplasts. Grana were the first structures discovered within the chloroplast by means of an electron microscope. Chlorophyll molecules are attached to the lamellae and the grana.
gravity : a natural force exerted on a body toward the earth's surface or between two bodies. Gravity has a strong effect on how matter interacts. Gravitational attraction depends on the masses of the bodies involved and the distance between them. Centrifugal force caused by the earth's rotation on its axis tends to lessen the force of gravity. The equatorial gravitational value at sea level (ye) is 9.780318 m-s and to calculate standard gravity at sea level; y = ye (1 + b1 sin2f = b2 sin2f), where f is geographical latitude b1 =5.3024 x 10-3 and b2 = 5.9 x 10-6
gravity wave : a wave disturbance in which buoyancy acts as a restoring force on parcels displaced from hydrostatic equilibrium.
gray (Gy) : The SI unit of absorbed dose of ionizing radiation equal to the energy in joules absorbed by one kg of irradiated material.
Greenhouse Effect : The phenomenon in which outgoing infrared radiation that would normally exit from a planet's atmosphere but instead, is trapped or reflected because of the presence of the atmosphere and its components is called the greenhouse effect. It has been calculated that this effect is necessary to maintain the earth's climate and surface temperature and, more importantly, the liquid state of water in the majority of the earth's biosphere; however, the best scientific estimates to date suggest that increasing amounts of greenhouse gases are resulting in higher temperatures worldwide. This could result in melting of icecaps that would raise the sea level and cause devastating floods in coastal areas, more extremes in rainfall and intensity, and the distribution of species in the biosphere.
greenhouse gases : Those atmospheric components that absorb strongly in the infrared region of the spectrum. Infrared radiation is reflected and emitted by the earth's surface as heat and causes a fairly large warming effect when trapped by these gases in the atmosphere. In order of abundance and importance as greenhouse gases are water vapor, carbon dioxide, ozone, nitrous oxide, methane, and chlorofluorocarbons (CFCs).
greenhouse warming : See global warming.
grey crescent : A surface region in the newly fertilised eggs of frogs and salamanders from which the orientation of the developing embryo can be ascertained.
growth : Enlargement in size of an organism, due to an increase in the number of cells, enlargement of cells already present, or both.
guanine : A purine base occurring in nucleic acids. Abbreviated G for the free base, rG for guanidine, and dG for deoxyguanidine.
guanosine :
Gulf Stream : a powerful current in the Atlantic Ocean. Its movement is related to density distribution system of waters and currents. Beginning in the Gulf of Mexico, it flows along the east coast of North America and across the Atlantic to Europe. The Gulf Stream carries warm water from the tropics and warms the climate of the land near where it passes.
gymnosperm : A member of the group of plants (mainly trees) that bear seeds that are not enclosed in an ovary.


habitat : The surroundings in which an organism resides - the organisms "address" in the biological community.
hadron : Any elementary particle that takes part in strong interactions. The group thus includes all baryons and mesons but not leptons or the photon.
haemoglobin : a red, iron containing protein pigment in erythrocytes that transports oxygen and carbon dioxide.
half-life : the amount of time taken for the number of parent nuclei to reduce to half its original number. The half-life of an isotope is inversely related to its decay constant.
hallucinogens : Drugs that produce hallucinations due to their stimulant action on the brain. Such drugs are also described as psychedelic. The ability of any given hallucinogen to produce a hallucination depends very much upon the personality of the individual. Some unlikely drugs, such as digitalis, may produce hallucinations in susceptible individuals.
halocline : In the oceans, a well-defined vertical gradient of salinity.
halogens : The group seven elements.
halophiles : bacteria which grow in a high molar concentration of NaCl. Their cell walls normally disintegrating at NaCl concentrations of less than 1.5M.
haploid : a condition in which an organism, or single cell, bears only one copy of each gene. Most higher organisms have two copies (alleles) of the gene for any given character and thus are called diploid. Many micro-organisms, however, such as bacteria, Paramecium, and most algae, are haploid during most of their life span.
Hardy -Weinberg law : the generalisation that the frequencies of both genes and genotypes will remain constant from generation to generation in a large, freely breeding population. This law is stated mathematically as the expansion of the binomial, where on member of a pair of alleles is designated p, and the other q: p2 + 2pq +q2 = 1.0. This mathematical expression means that the frequencies of the alleles symbolised as p and q remain constant (at whatever their initial values) from generation to generation, as long as the conditions mentioned above prevail. This law is also sometimes referred to as the law of genetic equilibrium.
Hartley-Huggins Band of ozone absorption : this spectral band in the UV is responsible for the absorption and filtering of solar ultraviolet radiation. Photons with a wavelength longer than 210 nm are weakly absorbed by oxygen in the atmosphere. Ozone then becomes the major UV absorber, with a band of 210-380 nm. Compare to ozone's Chappuis band in the visible wavelength region.
hazard : The inherent property of a substance capable of causing harm (e.g. toxicity, radioactivity, flammability, explosivity).
haze : an atmospheric aerosol of sufficient concentration to be visible. The particles are so small that they cannot be seen individually but are still effective in visual range restriction. The Blue Ridge Mountains of the Eastern United States have a haze caused by the natural emissions of hydrocarbons (mostly isoprene-see below) which are oxidized and form aerosols.
heat flux : The amount of heat that is transferred across a surface of unit area in a unit of time.
hecto (h) : 102
heliocentric distance (r) : The distance of an object from the sun, usually given in astronomical units.
heme : A complex molecular structure ( a porphyrin ring) in which a central ion is capable of undergoing repeated oxidation and reduction. The heme structure is the basis of such important biological molecules as haemoglobin, myoglobin and the cytochromes.
henry (H) : Unit of inductance which gives an electromagnetic force of one volt in a closed circuit with a rate of change of current of one ampere per second.
Henry's Law : The relationship that defines the partition of a soluble or partially soluble species between the gas and solution phases. It is often represented as Hc. It is the relationship of species dissolving but not reacting in solution to those in equilibrium in the gas phase. The equation used for this is: [Caq] = [Hc]*[Cg ]. Hc is the Henry's Law Constant. This may be regarded as a measure of the molecules in a gas to those dissolve in solution, and this relationship is temperature dependent. Cg and Caq are the concentrations or partial pressure of species C in gas and aqueous solution, respectively.
herbivore : An organism whose diet consists exclusively of vegetation.
hermaphroitism : A state characterised by the presence of both male and female sex organs in the same organism. An individual with both male and female sex organs is called a hermaphrodite.
heroin :
hertz (Hz) : Unit of frequency equal to one cycle per second.
Hess's Law :
heterogametes : Two gametes, structurally dissimilar, capable of fusion to form a zygote. The sperm and the egg are examples of heterogametes.
heterogamy : The condition in which gametes are differentiated into two distinct forms (generally male and female).
heterosexuality : Sexual attraction and/or intercourse between members of opposite sexes.
heterotroph : An organism that depends on its environment for a supply of nutritive material to build upon its own organic constituents and also for general energy requirements.
heterozygous : Term for the condition in which the two members of a pair of genes located on homologous chromosomes and influencing a given characteristic are different.
high-performance liquid chromatography (HPLC) : an analytical method used to determine the amount of a compound in various media such as the air, water or blood. Samples of the desired media (air, water, etc.) are dissolved in solution and then the components are separated by injecting the solution through a mobile phase solution and then a stationary phase solution. As the solution passes through the stationary phase, the components are separated out due to different partitioning behaviors between the components in the mobile phase and the stationary phase. This allows each component to be analyzed separately as they pass through the detector.
histamine : A chemical produced by the body when a tissue is irritated by an antigen reaching and causing irritation to tissue cells.
histology : The study of tissues.
histone : A type of protein rich in basic amino acids that is found in the chromosomes of all eucaryotic cells except sperm.
HOLAB : Home Office Laboratory form. From filled in by Office(s) involved in a certain case and containing a list of items submitted to the FSS for analysis. Found in the casefile.
H.O.L.M.E.S. : Home office large major enquiry system.
holmium (Ho) :
Holocene epoch : The present or recent epoch in geological time, including the last 10,000 years. It is sometimes called the Post-galacial, although some authorities consider it only an interglacial phase of the Pleistocene. At the beginning of the Holocene the general rise in sea-level, resulting from the melting of the ice, isolated Britain from the rest of Europe. homeostasis, The dynamic equilibrium processes which maintain a relatively constant internal environment in the face of variations in the external environment.
homologous : In anatomy, the term applied to body parts that are similar in structure but not necessarily in function, such as the human arm and the foreleg of a horse.
homologous chromosomes : The pair of structurally similar chromosomes within a diploid cell which carry inheritance factors influencing the same traits.
homosexuality : Sexual attraction and/or intercourse between members of the same sex.
homozygous : Term for the condition in which two pairs of genes located on homologous chromosomes and influencing a given characteristic are identical.
hormone : A chemical substance produced in small quantities in one part of an organism. Chemically, hormones may be proteins (insulin), steroids (oestrogen's) or small metabolites (thyroxin).
Hubble's law : The velocity of an object moving away from the observer in space is proportional to it's distance from the observer.
humic Acid : Occurs in rotting vegetable matter and is abundant as a constiuent of freshwaters as a consequence of soil runoff. Humic acid is not a simple chemical species, but a designation for a group of very large molecules derived from lignin and other actual materials.
humidifier fever : A flu-like illness caused by inhalation of fine droplets of water from humidifiers that have become contaminated.
humidity : The moisture content of air. Relative humidity is the ratio of the amount of water vapor actually present in the air to the greatest amount possible at that same temperature.
humus : Rich dark organic material which is formed by the decay of dead leaves and plants and is essential for fertilising the soil.
Hunter's syndrome : An inherited disorder of mucopolysaccharide metabolism (less serious than Hurler's syndrome) which allows the accumulation of certain mucopolysaccharides in connective tissue. No corneal clouding is seen, and very few examples of dwarfism. The gene for Hunter's syndrome is an x-linked recessive.
Hurler's syndrome : An inherited disorder of mucopolysaccharide metabolism in connective tissue, resulting in a serious malfunction of the skeleton, including dwarfism. Deafness and clouding of the cornea also occur. Results from lack of production of the enzyme glucose -6- phosphate dehydrogenase, thus allowing a build up of mucopolysaccharides. The gene for Hurler's syndrome is an autosomal recessive.
hyaloplasm : part of the cytoplasm hydrocarbon, An organic compound that contains only Carbon and Hydrogen.
hydrocarbons : chemicals containing only carbon and hydrogen. These are of prime economic importance because they encompass the constituents of the major fossil fuels, petroleum and natural gas, as well as plastics, waxes, and oils. In urban pollution, these components, along with NOx and sunlight, contribute to the formation of tropospheric ozone.
hydrogen bond : a weak attraction (much weaker than a covalent or ionic bond, but much stronger than Van der Waals' forces) between an oxygen, nitrogen, or fluorine atom in one molecule and a hydrogen atom in a neighbouring molecule. The hydrogen atom must itself be linked to a similar electronegative atom by a covalent bond. The attraction arises because the atom bonded to the hydrogen atoms exerts a strong pull on the shared electrons and thus confers a partial positive charge on the hydrogen. Consequently electrostatic attraction occurs between this hydrogen atom and the oxygen, fluorine, or nitrogen in the other molecule. Hydrogen bonding is responsible for maintaining the structure of proteins and nucleic acids.
hydrogen bromide - HBr : in the stratosphere, ozone is continuously being formed via the Chapman mechanism. However, halogen radicals such as bromine and chlorine (released from anthropogenic and some natural sources) catalyze the breakdown of ozone which results in a net ozone loss: O3 + Br----> BrO + O2 A reservoir species is a compound whose formation breaks the destruction cycle by taking the halogen radical out of the cycle. Two examples are HCl and HBr. Unfortunately, the success of HBr as a reservoir species is very limited due to the fact that it photodissociates quickly and easily. Thus, the ozone depleting effects of bromine are, atom for atom, more severe than those of chlorine.
hydrogen chloride - HCl : anhydrous hydrochloric acid. Its molecular weight is 36.47 g/mol; it is a colorless, corrosive gas. Hydrogen chloride is a covalent bonded nonflammable gas and ionizes almost completely when dissolved in water. When dissolved in water, hydrogen chloride forms a strong acid, hydrochloric acid. In the stratosphere, HCl acts as a reservoir species temporarily removing chlorine radicals from a catalytic ozone destruction cycle. (See ozone and chlorine.)
hydrochlorofluorocarbons - HCFCs : chemical species slated to replace CFCs in the near future in most Western nations. When the normal chlorofluorocarbons (see above) reach the stratosphere and are photo-decomposed, their released chlorine radicals destroy the natural ozone that acts as our umbrella to shield the Earth from ultraviolet radiation (see chlorine and ozone). With one or more hydrogen-carbon bonds, HCFCs are still useful as replacement for CFCs in most applications. However, this bonding structure makes HCFCs much more chemicallyy unstable, as compared to CFCs, and therefore subject to hydroxyl radical and ozone attack early in their gas phase career in the atmosphere. In fact they react in the troposphere instead of the stratosphere. Their atmospheric lifetime is shorter than CFCs and they, therefore, have a smaller chance of reaching the stratosphere where their chlorine could be released by destructive photolysis and enter the catalytic ozone destruction cycle.
hydrogen peroxide - H2O2 : this compounds molecular weight is 34.02g/mol; it is a colorless, rather unstable oxidant with a bitter taste and caustic to the skin. Hydrogen peroxide will decompose, liberating oxygen. Pure hydrogen peroxide is stable, but the slightest impurity will enhance decomposition, often violently. Concentrated solutions of hydrogen peroxide are highly corrosive and toxic. H2O2 is used as bleach, deodorizer, and in the manufacturing of rocket fuel. The hydrogen peroxide in your bathroom is approximately 3 percent in water. In the atmosphere this is probably one of the oxidizers for sulfur dioxide in cloud water droplets that produces sulfuric acid, a major component in acid rain.
hydrogen sulphide - H2S : hydrogen sulphide is a reducing species, which is relatively unstable but survives for rather a long time owing to its slow reaction with atmospheric oxygen. This sulfur-containing gas is a major participant in gas to particle conversion in the atmosphere. Many sulfur-containing gases are reactive and thus are rapidly converted to sulfuric acid. hydrolysis, The chemical breakdown of a larger molecule into smaller units by the addition of water.
hydrometeors : any condensed form of water, larger than a single water molecule, that is falling or suspended in the atmosphere; some examples of hydrometeors are snow, fog, cloud or rain. When these particles reach the size of 10-20 micrometers, available water is depleted and a stable cloud is formed.
hydroperoxy radical - HO2 : this radical readily reacts with nitrogen oxides and hydrocarbons in the atmosphere; in urban atmospheres, the major source of the hydroperoxy radical is formaldehyde photolysis.
hydrophilic : having a tendency to bind water molecules.
hydrophobic : a substance having a strong tendency to reject association with water.
hydrosol : A dispersion of solid particles is a liquid system.
hydrosphere : That part of the atmosphere which contains water in the liquid, solid, or gaseous phase.
hydrostatic : a vertical balance between gravity and the vertical pressure gradient force. The atmosphere is considered to be in hydrostatic balance except in strong disturbances. i.e. thunderstorms.
hydrothermal chemistry : aqueous chemistry under high temperature conditions. In biospheric chemistry, this refers to water whose chemical composition has been altered by deep, hot rock and which tends to come to the surface at fault lines. This creates boiling springs and geysers.
hydrostatic pressure : In the circulatory system of animals the pressure created by the pumping action of the heart. Hydrostatic pressure aids in forcing water out of the capillaries and into interstitial spaces.
hydroxyl radical - OH : a radical consisting of one hydrogen atom and one oxygen atom which does not normally exist in a stable form; this radical readily reacts with methane and carbon monoxide. The source of the hydroxyl radical in the atmosphere occurs primarily through the 1) photolysis of hydrogen peroxide, heat, and light and 2) the attack on water of an excited oxygen radical (created by the photolysis of ozone).
hygroscopic : having the characteristic of drawing moisture from the atmosphere.
hypertension : high blood pressure.
hypostasis : the process that sets in immediately after death and which is also referred to as post mortem lividity or livor mortis.
hypothesis : a tentative explanation suggested to account for observed phenomena.
hypsometric diagram : a graph that shows in any way the relative amounts of Earth's surface at different elevations with regard to sea level.
hypsometry : a technique of mapping the elevation contour of both land and the ocean floor using tinting to illustrate a change in contour.
hyoscine : vegetable drug occurring naturally in deadly nightshade, thorn apple and henbane. It is commonly called scopolamine to distinguish it from hyoscyamine.
hyperfocal distance : A lens may be focussed at a distance less than infinity, but, so that points at infinity remain in acceptable focus. In this way the greatest possible depth of field ( in terms of subject in acceptable focus) is achieved.
hypostasis (lividity) : The process whereby the blood sinks to the lowest part of the body, and which starts immediately at the onset of death. The red corpuscles tend to settle first, giving the area a livid colouration. Between one and three hours after death the discolouration becomes patchy and bluish in colour, at around eight hours the patches have fused together in large purple-black areas. If pressed the skin will blanch. When the blood coagulates in the vessels after 10-12 hours the purple stain will become fixed and no longer blanch under pressure.


Ice age : period in the earth’s history when ice spread towards the equator with a general lowering of temperatures. The most recent of these was the Pleistocene epoch ending about 10,000 years ago, during which four major advances of ice occurred. Other ice ages occurred in Permo-Carboniferous times about 250 million years ago and Pre-Cambrian times, about 500 million years ago. Between 1550 and 1850 the little ice age occurred, with significant lowering of temperatures in the Northern hemisphere.
ideal gas : A hypothetical gas that exactly obeys the ideal gas equation. Such a gas has no inter-molecular forces and the volume of it’s molecules is negligible. Also known as a perfect gas it is closely approximated by real gasses at low pressure.
ideal gas equation :
PV = nRT where P= the pressure of gas (Pa), V = volume of gas (m3), T = temperature of gas (K) and n= number of moles of gas present. R is the universal gas constant and has a value of 8.3145 J mol-1 K-1 .
IdO/OIC : Identifying Officer. Officer involved in case (Officer In Charge).
igneous rock : One of three major categories of rock consisting mostly of crystalline rocks cooled directly from magma. That cooled at the surface forms extrusive rocks - volcanic lavas with small crystals because they have cooled rapidly. Some extrusive rocks, such as obsidian, are like glass. Igneous rocks cooled at depth are called intrusive or plutonic. They have larger crystals, granite being a common example. A third category contains the hypabyssal rocks, cooled in dykes or sills at an intermediate depth and usually having intermediate crystal sizes, for example dolerite. Silica is the dominant chemical constituent of igneous rocks and the silica content, resulting from the chemical composition of the magma from which the rock cooled, determines whether the rock is acidic (over 66% silica), intermediate (55-66%), basic (45 -55%), or ultra basic (under 45%).
immunology : The field of biology dealing with the process whereby organisms develop a chemical resistance within their bodies to various types of foreign substances (bacteria, pollen, etc.).
inflorescence (botany) : The grouping of flowers on a plant.
imprinting : The rapid fixing of social preferences; for example the tendency of a duckling to follow the first moving object that it sees after hatching.
inclusion : any of a number of non-living structures occurring within the cytoplasm of a cell.
indifferent species : any species that has no particular preference for community.
inductive logic : A process whereby a conclusion is reached by proceeding from specific cases to a generalisation.
infra red radiation : electromagnetic radiation with wavelengths between about 750 nanometres and 1 millimetre. In the electromagnetic spectrum it lies between the end of visible light and microwaves. Infrared radiation is emitted by all bodies of temperatures above absolute zero and is the predominant radiation emitted up to temperatures of about 3000o C.
instability : possessing the ability to move away from the original position; allows convection and enhances vertical motions.
innate behaviour : Ethological term that replaces the concept of instinct. In general, innate behaviour is that which is presumably inherited to a large degree.
insectivore : An animal that feeds on insects and other small creatures, or a plant that traps and absorbs insects.
instinct : Term applied to behaviour that is primarily genetic in nature and seems less amenable to change through learning. Most behaviourists prefer to use the term “innate behaviour” rather than “instinct”.
interference : A wave phenomenon in which two waves combine either to reinforce each other or to cancel each other out, depending on their relative phases. The pattern of light and dark strips so produced is called an interference pattern (or interference fringe). The effect occurs when the two beams have the same frequency and have approximately the same amplitude.
internal environment : The conditions generated inside an organism by the functions and interactions of cells, tissues, organs and systems.
interphase : The longest individual phase of mitosis, often considered the resulting phase between two active cell divisions, during which the genetic material of the cell is being duplicated.
interpolation : filling in a value on a graph between two given values.
interstitial cells : In the mammalian testes, cells that produce and secrete the male sex hormones.
inversion : temperatures increasing with increased altitude, or height. A negative lapse rate.
inversion : The process of chromosome breakage and rejoining in such a way that a whole segment breaks from a chromosome and is replaced in reverse order. Thus if a sequence of genes on a normal chromosome were represented as ABCDEFG;         , and two breaks occurred , one between  and  and the other between and, the middle segment  might turn and rejoin in reverse direction, so that the sequence of genes on the chromosome would read 
invertebrates : Organisms characterised by the lack of a notochord. Invertebrates compose approx. nineteen animal phyla.
in vitro : Used in reference to an experiment done in a cell-free system.
in vivo : Used in reference to an experiment done in living sells.
involucre : A series of bract like leaves below a cluster of flowers.
ion : an atom, or group of atoms that has lost or gained one or more electrons and consequently has an electric charge. Positively and negatively charged ions are called cations and anions respectively. The sign and magnitude of the charge is indicated by a superscript, as in the potassium ion K+, or the doubly charged sulphate ion, SO42-. Many compounds (electrovalent compounds) are ionic.
ionic bond : Where an outer electron is transferred from one atom to another so that ions are formed. The electrostatic force between the ions hold the molecule or crystal together. For example, a molecule of sodium chloride (NaCl) is formed when the single electron in the outer shell of the sodium atom is transferred to the chlorine atom. As the chlorine atom has seven electrons it gives it the eight electron argon stability.
ionic strength : A measure of the total amount of free charges per unit volume; for example, a divalent ion contributes twice as much to the ionic strength of a solution as a monovalent ion.
ionization potential : The minimum energy required to ionise an atom. It is measured in electron volts.
iota ( I, i ) :
iridescent : Having glittering, changing colours.
irruption : An irregular migration.
islet cells : Specialised cells of the pancreas that synthesise insulin or glucagon.
isobar : a line of constant pressure.
isodrosotherm : a line of constant dew point temperature.
isoheight : a line of constant height above a certain reference point such as sea-level. Also called a contour line.
isogametes : Two gametes which are morphologically alike and capable of fusion to form a zygote. They are not visibly differentiated into male and female forms.
isolating mechanisms : Differences introduced by speciation and divergence during geographic isolations of two populations which prevent inter-breeding should the populations come back together. Such mechanisms include seasonal isolation, ecological isolation, physiological isolation, and behavioural isolation.
isotach : a line of constant wind speed.
isotherm : a line of constant temperature.
isotope : Atoms containing different numbers of neutrons, i.e. having the same atomic number but different mass numbers.
isotropic : Having a physical property independent of direction.


jaborandi : An American tropical plant from the dried leaves of which can be extracted pilo carpine, an alkaloid used medicinally in eye drops to constrict the pupil and treat glaucoma.
jaundice : Yellowing of the skin and whites of the eyes due to a presence of bile pigments. Bile pigments are usually produced in the liver from the breakdown of red blood cells and then excreted in bile into the gut. Jaundice may result if there is excessive breakdown of red blood cells, as in haemolytic anaemia, or in disease of the liver, such as hepatitis or blockage of the bile duct by gallstones.
jejunum :, Part of the small intestine between the duodenum and the ileum.
Jet Stream : the major atmospheric air currents that are the result of a strong meridional pressure gradients.
Joule (J): Defined as a SI unit which expresses a unit of energy. 1 J = 1 kg*m2/s2.
joule : Unit of work or energy equivalent to the work done b a force of one Newton when its point of application moves one metre in the direction of the action of the force. Also the work done or heat generated by a current of one ampere flowing for one second against a resistance of one ohm.
Joule-Kelvin effect : The change in temperature of a gas when it is expanded adiabetically. In most gasses it produce a cooling as energy is needed to overcome the attractive forces between molecules when the gas is expanded. The effect is utilised in refrigeration and in the liquefaction of gasses.
Jupiter : The fifth planet from the sun and the first of the giant planets with an equatorial diameter 142,800 kilometres (pole to pole 133,500 kilometres) and a mass of 2 x 1024 tons. It's density is 1.34 times that of water. It orbits the Sun every 12 years but, despite it's size rotates in a period of once every 9 hours 55 minutes 30 seconds. The magnetic field on Jupiter is ten times that of the Earth's and contains 20,000 times as much energy. The axis of the magnetic field is tilted 11 degrees from the planets rotation axis and is offset from the centre of Jupiter in a manner similar to the axis of the Earth's field.
It is the prototype of the giant, gas-rich planets which must, from their low density, have a composition fundamentally different from that of the inner planets. One theory is that the interior of Jupiter includes a large core of metallic hydrogen. It emits twice as much energy as it receives from the Sun and the temperature at the centre of the planet may be 30,000° C. Jupiter also has 16 moons and a faint ring system and has been described by some as a failed star.
Jurassic period : A geological period of the Mesozoic era, between about 2 and 1.35 x 108 years ago. The dinosaurs and other reptiles flourished and diversified in this period. Fossils of the earliest birds and mammals have also been found in Jurassic rocks.


k-strategists :
kappa ( K, k ) :
karyotype : Characterisation of the chromosome complement of an individual organism with regard to the number, size, and shape of chromosomes present. Karyotypes are usually displayed as a series of chromosomes lined up in a specific order, showing each of the chromosome pairs present (including extra or missing chromosomes).
Katabatic winds : Strong winds associated with mountains and valleys. They occur when cold, dense air is produced by radiational cooling flows downhill due to the pull of gravity to a lower, warmer region such as depressions and valleys.
kava : A shrub, Piper methysticum, the roots of which can be ground and fermented to make a narcotic drink. It has been used medicinally as a local anaesthetic.
Kelvin (K) : The SI unit of temperature equal to 1/273.16 of the thermodynamic temperature of the triple point of water ( 0K = -273.16oC ).
Kelvin Scale : scale for measuring temperature that sets zero degrees at the point of which molecular motion desists, that is, the point at which there is no heat. It is also known as the absolute scale.
keratin : an insoluble fibrous protein that is the major constituent of hair, nails, feathers, beaks, horns and scales. Keratin is also found in other protective layers of the skin.
ketone : A class of organic chemicals having the general formula RCOR', where R and R' are hydrocarbon groups. Ketones are prepared by the oxidation of secondary alcohols. Acetone (dimethyl ketone) is a common example.
kieselguhr : a porous form of silicon dioxide (SiO2) which is added to nitroglycerine to make dynamite.
kilo (k) : 103
kilocalorie : the amount of heat required to raise the temperature of one kilogram of water from 14.5 to 15.5. The kilocalorie is used to measure the metabolism (energy turnover) of animals.
kiloton : A measure of the explosive power of a nuclear weapon. A kiloton is equivalent to an explosion of 1000tons of trinitrotoluene (TNT).
kinetics : the study of the rates at which chemical reactions occur and the influence of physical and chemical conditions of these rates.
kinetics : the factors involved in governing the velocity of an enzymatic reaction.
kinetic energy : Energy of motion or energy in the process of doing work.
kinetic molecular theory (kinetic theory) :
kinetic stability : the stability of a molecule conferred by the slow rate of its decomposition.
kinetochore (centromere) : the region of a chromosome at which the chromatids remain connected following chromosome replication and to which the spindle microtubules appear to be connected during cell division.
klystron : An electronic device used to generate or amplify microwaves. It consists of a sealed evacuated tube in which a steady beam of electrons from an electron gun is alternatively accelerated and retarded by high frequency waves (velocity modulation) as it passes through a cavity. The resultant radio frequency pulses are picked up at the second cavity, either as a frequency oscillation or, if connected to a waveguide, as electromagnetic waves. The second cavity can be tuned to the frequency, or a harmonic of it.
KM ( Kastle – Meyer. ) : Name of inventor of test used to identify blood. ( Presumptive test only, not definitive ).
knot : unit of speed used for ships and aircraft and equivalent to one nautical mile (1.15 miles) per hour.
konimeter : an instrument utililized to determine the amount of dust particles in a sample of air.
Krakatoa Winds : the winds produced as a result of the Krakatoa eruption on the island of Krakatoa in 1883. This volcanic blast is the largest in recent times whose effects caused several atmospheric changes such as lowering the global temperature by 1.2 degrees Celsius and changing tides and wind conditions and providing red sunsets as far away as the United States.
Kreb's cycle (citric acid or tricarboxylic acid cycle) : the sequence of chemical reactions, taking place in the mitochondria of the cells, that is central to the metabolism of virtually all living organisms. The cycle involves the conversion of acetyl coenzyme A, derived from the carbohydrates, proteins, and fats of food, into hydrogen atoms or electrons, from which the usable energy in the form of ATP is produced by the cytochrome electron transport chain. Intermediate products of the Kreb's cycle are used for the manufacture of carbohydrates, lipids and proteins by cells.
Kurcatovium (Ku) : the name given to Rutherfordium by the Russians who claim to have discovered it first, in some reference works element 104 is referred to as kurcatovium (Ku).


labia : In human female genitalia, the thin, pink folds of epithelial tissue that lie lateral to the vaginal opening. Homologous to the male scrotum. There are two labial structures; labia minora and labia majora.
Lamarckism : An evolutionary theory proposed in the 18th century and consisting of several ideas which include; Because of new physical needs, new structures arise an old structures are modified; use or disuse of parts causes variation in a structure; and acquired characteristics can be transmitted to succeeding generations.
lambda ( L, l ) :
lamellae : Membranous sacs stacked parallel to each other within the chloroplasts of green plant cells. There are two types of lamellae; stroma lamellae and grana lamellae. Together they are the sight of the light reactions in photosynthesis.
lanthanides : The group of elements from No.57 to 71 inc.
lapse rate : The theoretical rate of decrease of temperature with increasing height in the atmosphere. If heat is neither gained nor lost from the air parcel under consideration, then the lapse rate is said to be adiabatic. For air parcels of differing water content this value is different.
larva : An intermediate free-living form of some organisms. In this stage the organism eats extensively and stores food. It then undergoes metamorphosis into the adult form, using the stored food as an energy source.
latent heat : If a change of state occurs from gas to liquid or liquid to solid, internal energy in the form of heat is released. If a change of state occurs from solid to liquid or liquid to gas, heat is required. Different compounds absorb and release different amounts of latent heat. Water releases nearly 600 kilocalories for each kilogram of water condensed.
latent heat : the heat either released or absorbed as a result of a change of state.
laudanum : Tincture of opium.
LC 50 : The calculated concentration of a substance that causes death in 50% of a population under prescribed conditions in a prescribed period of time (normally expressed as ppm or mg/m3 for gases, mg/l for liquids).
LD 50 : The calculated dose of chemical (mg per kg body weight) causing death in 50% of test population. (The species of animal, route of administration, any vehicle used to dissolve or suspend the material, and the time period of exposure should be reported).
Legionnaires Disease: Infection caused by inhaling a fine spray of airborne water carrying Legionella pneumophila bacteria.
lifting condensation level (LCL) : The level at which lifted air will saturate.
lead poisoning,
Le Chatelier's principle : The model that states that " a system in equilibrium, when subjected to change in one of the factors (temperature, pressure or concentration) will alter it's equilibrium so as to nullify, as much as possible, the change in conditions.
lepton : A group of elementary particles, consisting the electron, muon, tau particle, neutrons and their antiparticles. They take part only in the weak and electromagnetic interactions; together with quarks and photons they are thought to be the only elementary particles.
leucocyte : A white blood cell.
leucoplast : A colourless plastid, thought to serve as a cytoplasm centre for the storage of certain materials, such as starch.
level of free convection (LFC) : The level at which lifted air becomes unstable and hence rises on its own.
ligand : A small molecule that binds to a larger one.
light : The form of electromagnetic radiation to which the eye is sensitive. It forms the part of the electromagnetic spectrum from 740 nanometres (red light) to 400 nanometres (blue light), white light consisting of a mixture of all the colours of the visible spectrum.
light, speed of : 2.997 925 x 108 ms-1
light year : A unit of measurement for a distance equivalent to 9.448 x 1015 metres, i.e. the distance travelled by light in one year.
linkage : The location of two or more genes on the same chromosome, so that the two characteristics are passed on together from parent to offspring.
lipids : A group of organic compounds including the fats and fat-like compounds of the steroids.
lipoprotein : A protein to which a lipid is covalently attached.
Lithology : branch of mineralogy that deals with the study of rocks and their composition.
Lithosphere : the outer, rigid shell of the Earth, situated above the asthenosphere and containing the crust, continents and plates.
lividity (livor mortis) : The process whereby the blood sinks to the lowest part of the body, and which starts immediately at the onset of death. The red corpuscles tend to settle first, giving the area a livid colouration. Between one and three hours after death the discolouration becomes patchy and bluish in colour, at around eight hours the patches have fused together in large purple-black areas. If pressed the skin will blanch. When the blood coagulates in the vessels after 10-12 hours the purple stain will become fixed and no longer blanch under pressure.
logarithm : The power to which a given number (the base) must be raised in order to equal a given number.
logarithmic phase : The phase of most rapid increase in size for a population; that is, the area of exponential increase on a sigmoid curve.
long-period comets : Comets moving in orbits having periods greater than 200 years.
longitudinal strain : The extension per unit length when a body is stretched.
loop of Henle : part of the kidney.
Lower Flammable (or explosive) Limit ( LEL ) : The lowest concentration of vapor/gas in air at a given pressure and temperature the will propagate a flame when exposed to an ignition source.
LPG (Liquid Petroleum Gas) : is a mixture of short hydrocarbons with most of the volume being propane and butane. LPG is considered an alternative fuel that burns cleaner than gasoline because of the very short hydrocarbon chains that tend to not produce a high volume of CO2, NOx radicals. LPG is now being found in the air in the unburned state most likely from leaking pipes and tanks, in this physical state LPG is now being seen a contributor to urban air pollution.
lumen (lm): Unit of luminous flux equivalent to the flux per unit solid angle from a uniform source of one candela.
luteinizing hormone : A hormone secreted in vertebrates by the anterior lobe of the pituitary gland of both sexes. In females it stimulates formation of the corpeus luteum; in males it regulates production of testosterone.
lux (lx) : Unit of illumination equivalent to one lumen per square metre.
lysins : A class of substances produced by sperm to dissolve the protective egg membranes and allow the sperm to enter and fertilise the egg.
lysis : The chemical breakdown of a cell, usually under the influence of enzymes released by the rupture of a lysosome, or by reproduction of viruses within the cell.
lysosome : A sac-like structure containing enzymes that catalyse the breakdown of fats, proteins, and nucleic acids. The membranes of lysosomes protect the cell from being digested by its own enzymes (autolysis). Lysosomes also serve as defence mechanisms, ingesting and digesting foreign toxic agents within the cell.
lysozyme : An enzyme that lyses certain bacteria by cleaving a polysaccharide component of their cell walls.


machine gun : A small arm that fires repeatedly without reloading. macrodactyly, fingers that are abnormally long.
macromolecule : A large molecule built up from smaller repeating units. Cellulose is a built up of repeating b-glucose units.
macroscale : a large scale event usually measured in 10,000's of kilometres and weeks of time; a planetary scale event; e.g. long waves in the jet stream.
magnitude (m1 and m2 for comets) : One of the most important pieces of information gathered by amateur astronomers. This represents the estimated brightness of the comet when compared to stars around it. The term "m1" is used to represent the total or integrated brightness of the comet's coma, while "m2" represents the brightness of the nucleus. Observers estimate "m1" by usually memorizing the comet's appearance and then defocusing the surrounding stars to a size equivalent to the comet's coma diameter. The memorized comet's appearance is then compared to the defocused stars to determine the comet's brightness. In meteor astronomy the magnitude of a meteor is compared to that of other stars in the sky. The magnitude scale is set up so that the brighter magnitudes are actually represented by smaller numbers. The sun is about magnitude -26, the moon -12, Venus is -4, and the faintest naked-eye star is generally about +6.
magnetron : An electronic device used to generate and amplify microwaves. It consists of a sealed evacuated tube containing a central cylindrical cathode (source of electrons) inside a cylindrical anode to which electrons are drawn by an electrostatic field. A steady magnetic field applied along the axis of the tube deflects the electrons from their radial path and, if strong enough, will cause them to rotate around the cathode setting up microwave frequency oscillations. It is widely used in radar generators.
major hazard : An industrial activity involving certain dangerous substances which have the potential to give rise to serious injury or damage beyond the immediate vicinity of the workplace.
mamma : pouch-like clouds, usually found beneath the anvil of a thunderstorm.
mapping (genetics) : The description of the physical order of a gene loci on a given chromosome, as determined by frequency of chromosome crossovers. The further apart two genes are on a chromosome, the greater the chance that crossing over will occur between them; thus the percentage of cross overs can be used to calculate the relative distances between genes. Chromosome maps established in this way can be correlated with actual chromosome structure by a variety of cytological techniques.
Marquis test : In the presence of most opium derivatives, but especially morphine and heroin, the reagent will turn purple As well as for opiates , the test is specific for amphetamines, which turn the reagent an orange brown.
Mars. Fourth planet out from the Sun, orbiting once every 686. 98 days at a distance varying between 1. 38 and 1. 67 astronomical units. Mars turns on it's axis once every 24 hours 37 minutes and 23 seconds. It has a diameter of 6,795 km (roughly half that of the Earth) and a mass a little more than one-tenth that of the Earth. It is a desert planet with a thin atmosphere (mainly carbon dioxide), where temperatures range from 26oC to -111oC.
Mars (Astronomy): The fourth planet from the Sun which it orbits every 687 Earth days. It's diameter is 4212 miles and it has approximately 0.38 of the Earth's gravity. One Martian day is 24 hours and 37 minutes long. The surface temperature ranges from about -84° C (-120° F) at night to 29° C (-20° F) in the afternoon and the water content of the atmosphere is less than 0.1 percent that of the air on Earth. The surface pressure of the atmosphere, which varies seasonally in accord with the evaporation of the polar caps, is only about 0.8 percent that of the Earth's atmosphere. The atmosphere is primarily Carbon Dioxide and there are two polar caps of frozen Carbon Dioxide. Mars has two moons, Phobos, 16.7 miles in diameter and Deimos, 9.3 miles in diameter.
marsupials : a primitive mammal belonging to the order Masupialia which lack a placenta and give birth to a very immature young which continue to be raised in the pouch of the mother until they are fully formed.
mass action, law of : The rate of chemical reaction for a uniform system at constant temperature varies as the concentration of each reacting substance, raised to the power equal to the number of molecule s in the substance appearing in the balanced equation. Thus, for the reaction 2H2 + O2 = 2H2O the speed of the forward reaction is in proportion to the concentration of (written [O2] and to [H2]2 H2; the reverse reaction depends on (H2O)2. The law is thus useful for calculation of equilibrium concentrations when reaction speeds are known and vice versa.
mass number (elements) : The number of protons and neutrons in the nucleus.
mass spectrometry : A process that sorts streams of electrically charged particles according to their different masses by using deflecting magnetic fields. The device that accomplishes this, a mass spectrometer, generally consists of a long tube that generates a magnetic field. The particles of varying masses are passed through the tube and the degree of deflection by the magnetic field is recorded on a photographic film at the other end. Given the strength of the field and the amount of deflection, investigators can calculate the relative masses of the particles. Isotopes of various elements can be detected by mass spectrometry.
matter : That which has weight and occupies space.
maximum exposure limit (UK) : The maximum concentration of an airborne substance (averaged over a reference period) to which employees may be exposed by inhalation under any circumstances. (Listed in Schedule 1 of COSHH Regulations).
McLeod guage : An instrument that uses Boyle's law to measure the pressure of a near vacuum. A sample of the vacuum is compressed into small volume, thus raising its pressure which may then be measured. It is accurate down to about 10-6 mmHg
mechanism : The philosophical view that life is explicable in terms of physical and chemical laws, and that the whole is equal to nothing more than the sum of its parts. Also called the mechanistic materialism.
mega (M) : 106
meiosis : A process of cellular division which results in each of the daughter cells containing half as many chromosomes as the parent cell (that is they are haploid). Meiosis occurs primarily in the formation of gamates or in spore formation in organisms such as ferns and mosses.
melanin : Any of a group of dark brown or black pigments occurring in the skin or other parts of the body.
melting point : The temperature at which the solid form of a substance becomes a liquid, normally at atmospheric pressure.
Mendel's laws : The basic principles governing the inheritance of characters.
First law : the Law of Independent Segregation, states that the factors of inheritance (alleles of the gene) that determine a particular characteristic segregate into separate sex cells.
Second law : the Law of Independent Assortment, states hat the segregation of factors for one character occurs independently of that for any other character. (This is true except for alleles of genes located on the same chromosome, which are segregated together).
Mercalli scale : A scale, from 1 to 12 used to measure the surface effects of earthquakes.
click here to go to scale
Mercury : Closest planet to the Sun, orbiting once every 87. 97 days at an average distance of 0.39 astronomical units. Mercury rotates once every 58. 64 days, so that three 'days' on Mercury last for two of the planet's 'years'. The planet is very heavily cratered, with essentially no atmosphere; temperatures range from 190oC to -180oC. Mercury has a diameter of 4,880 km (intermediate in size between the Moon and Mars) and a mass about 5% of that of the Earth.
Mercury : The innermost of the planets with a diameter of 3025 miles. It has been found to be closer to a perfect sphere than is the Earth. It has a weak magnetic field and a trace of atmosphere (one-trillionth the density of the Earth and composed chiefly of argon, neon and helium) and a gravity about 1/3 that of the Earth. The planet travels around the sun in an 88 day orbit which is more elliptical than any of the other planets except Pluto.
mercury poisoning :
meridional : in the north-south direction; along a meridian.
mesenchyme : An embryonic tissue derived from the mesodermal layer of an animal embryo. It appears on the embryo as a mass of scattered angular or pointed cells with long, protruding processes. In vertebrates the mesenchyme forms the connective tissues (bone, cartilage, etc.).
mesoderm : In vertebrate embryos, the third germ layer, lying between the ectoderm and endoderm and giving rise to connective tissue, muscle, the urogenital system, the vascular system, and the lining of the coelom.
mesopause : The upper limit and the coldest portion of the mesosphere. The transition zone between the mesosphere and the thermosphere.
mesoscale : a middle-sized event that usually is measured in 10's of miles and hours of time; a thunderstorm-sized phenomenon; e.g. thunderstorms and sea breeze circulations.
mesosphere : In the atmosphere, the region immediately above the stratosphere and innemdiately below the thermosphere. The mesosphere begins about 50 kilometers high at the stratopause and ends about 80 kilometers high at the mesopause. The temperature in the mesosphere decreases sharply with increased altitude.
Mesozoic era : The geological era containing the Triassic, Jurassic, and Cretaceous periods, and lasting from about 2.8 to 2.4 x 108 years ago. The reptiles were at their greatest development during this era but became extinct before the end of it. The Alpine orogeny began at the end of the era.
Mesozoic Period : Period spanning from 225 to 65 million years before present, this period was marked by widespread warmth of the planet's surface, especially in the higher latitudes. During this time the continents were joined in a single supercontinent. This situation most likely facilitated the meridional transport of heat by ocean currents, thus resulting in an even distribution of global heat.
messenger RNA (mRNA) : A strand of RNA synthesised in the nucleus of a cell with one DNA strand as a template. Thus mRNA has a base sequence directly complementary to the base sequence of the DNA molecule. After its formation , mRNA migrates from the nucleus to the cytoplasm, where it becomes associated with the ribosomes.
metabolism : The sum total of chemical and physical processes within the body related to the release of energy by the breakdown of chemical fuel and the use of that energy by the c ells of their own work.
metaceldehyde :
metamorphic rock :
metaphase : The phase of mitosis characterised by the lining up of the chromosome pairs along the equatorial plate of the cell.
metaphysics : A method of thinking which tries to go beyond the present physical reality and postulate the unknown. In metaphysics, phenomena are regarded as final, immutable, and independent of one another. Metaphysical thinking is generally contrasted to scientific thinking.
metastable state : A object that returns to its original position after force is applied.
meteor : Popularly called a "shooting star" or a "falling star", a meteor is actually an object usually ranging from the size of a dust particle to a rock that enters Earth's atmosphere, and is heated by the friction of air resistence. Most meteors originate from comets.
meteorite : A meteor that is large enough to survive its passage through the atmosphere and hit the ground.
meteorology : The science of the atmosphere and its direct effects upon the earth's surface. Meteorology is especially concerned with how atmospheric conditions effect the weather.
meteor shower : a shower of meteors occurs when Earth's orbit intersects the orbit of a meteor stream.
meteor storm : This is a rare event that occurs when Earth encounters closely grouped meteors within a meteor stream. Such events can see meteor rates exceeding 1000 per minute.
meteor stream : This represents the orbit of meteoroids as they travel around the sun. Meteors are the by-product of comets, so it is possible for the parent comet to be traveling in the same orbit--if it still exists.
meteor train : A trail of ionized dust and gas that remains along the path of a meteor.
METEOSAT (METEOrological SATellite) : Europe's geostationary weather satellite, launched by the European Space Agency and now operated by an organization called Eumetsat. METEOSAT transmits at 1691 and 1694.5 MHz.
methane (CH4) : a colorless, odorless, flammable, greenhouse gas. It is the simplest of all hydrocarbons with a formula of CH4. Methane is released naturally into the air from anaerobic environments such as marshes, swamps, and rice fields, and from symbiotic microbes in the guts of ruminant animals (such as cattle, sheep, and camels), and sewage sludge. Methane is released from methane producing bacteria (methanogens) that live in these anaerobic places. Methanogens in termite guts are the source of methane released by termites. The discovery that termites may be a significant source of atmospheric methane is attributed to work by Patrick Zimmerman and his research group members at the National Center for Atmospheric Research in Boulder Colorado (see reference immediately below and papers in the scientific literature).
methane flux : The (continuous) flow of methane from one place in the atmosphere to another. It is usually measured as a rate of flow across a given area where methane is produced; for instance, the average amount of methane being released from a rice field of a specific area every hour would be considered the methane flux rate for that field.
methanesulfonic acid (MSA) : This may be a significant component of atmospheric aerosol particles that form from the atmospheric oxidation of dimethylsulfide (DMS), when this DMS is produced by phytoplankton. These aerosol particles can lead to the formation of cloud condensation nuclei, water droplet formation, and hence clouds and storm formation. This therefore may contribute to the turbulent mixing of oceanic surface waters and subsequent upwelling of nutrients that feed those microorganisms (a positive feedback cycle). It is thought that increased emissions of dimethylsulfide, and subsequent methanesulfonic acid over the oceans from an increase in sea water temperature may have a negative feedback on global warming by increasing cloud formation; although the net effect of clouds on global warming is very unclear at this point.
methyl bromide - CH3Br : this halocarbon is released, to a degree, naturally from the oceans, but is more commonly released from its anthropogenic use as a soil fumigant or pesticide. Methyl bromide is persistent enough to reach the stratosphere where it photochemically decomposes to yield atomic bromine (radical) and proceeds to destroy stratospheric ozone in the same manner as the atomic chlorine radical. On an atom-for-atom basis, stratospheric bromine is more efficient at destroying ozone than is chlorine because the HBr reservoir species is more photochemically active than HCl; however, there is much less of hydrogen bromide in the stratosphere.
methyl chloride - CH3Cl : this compound supplies chlorine to the stratosphere by occasional volcanic eruptions and by tropospheric to stratospheric transport. Methyl chloride is also produced by seaweed. The natural chlorine content of the stratosphere as a consequence of these sources is about 0.6 ppbv.
methyl chloroform - CH3CCl3 : a synthetic organic compound that has been used as a substitute for earlier solvents that contributed to air pollution. Methyl chloroform is now known to cause destruction to stratospheric ozone and is scheduled to be phased out by the year 2005.
micro (m) : 10-6
microfilament : A minute protein fibre in the cytoplasm of certain cells, its function appears to be providing support and shape to the cell.
microscale : a small-sized event that is usually measured in meters and seconds to minutes; a cloud-sized phenomenon; e.g. turbulence, and dust devils.
microtubules : Tiny intracellular tubes composing such diverse structures as the spindle apparatus and the centrioles.
microwaves : Electromagnetic radiation with wavelengths between 1 and 300 millimetres, lying between infrared rays and radio-waves in the electromagnetic spectrum. They are used in radar and microwave heating. This method is used in the rapid cooking of food as the radiation penetrates to the interior of the food. The microwave photon is the same order of magnitude as he vibrational energy of atoms and molecules and therefore heats the interior directly, rather than by conduction from the surface. It is also used in sterilisation and drying wood etc. Microwaves are generated by such devices as magnetrons and klystrons.
Midocean Ridge : a major, elevated, linear feature of the seafloor, consisting of many small, slightly offset segments, with a total length of 200 to 200,000 km. This type of plate boundary occurs in a divergence zone, which is a site where two plates are being pulled apart and new oceanic lithosphere is being created.
mie scattering : Processes by which particles of similar size and electrical characteristics separate or disperse different wavelengths (read colors) of light. First described by Gustav Mie in 1808. Since the sun's visible spectrum contains a mixture of (traditionally ordered) red, orange, yellow, green, blue, indigo, and violet colors, these wavelengths are differentially scattered by particles as they travel through the atmosphere. Red, longer wavelength, light is scattered not much and blue, shorted wavelength, light is scattered much more. This is why the sky appears blue: the sun's blue light is scattered back towards your eyes from atmospheric particles so when you look up, that is, away from the sun, the light you see is light scattered to your eye from atmospheric particles. (You might ask yourself why the sky, viewed at an off angle from the sun, isn't black instead of blue.) Mie scattering is also the reason why sunsets appear red: the sun's red light is NOT scattered as much as blue light by atmospheric partricles and so solar blue light is scattered away from your eyes on its way from the sun and red light is scattered less. The result is that more solar red light hits your eyes than blue and sunsets appear red. Notice also that the redness of sunsets increases at the amount of atmospheric particles between you and the sun increase, that is as the sun "goes down" mie scattering increases as the amount of particles between you and the sun increases.
milli (m) : 10-3
minimal medium : A medium containing only those elements absolutely essential for the growth of a particular micro-organism, and which the organism cannot synthesise itself. Generally, minimal media contain a carbohydrate source, various inorganic salts, and sometimes a growth factor such as biotin.
minor meteor showers : meteor showers that produce less than 10 meteors per hour at the time of maximum activity.
Miocene epoch : The fourth epoch of the Tertiary period lasting from about 24.6 to 5.1 million years ago. It was a period of major earth movements and the Alpine and Himalayan orogenies took p[lace at this time.
miscarriage : An accidental or spontaneous abortion. They can occur anywhere from the trophoblast stage through to the eighth or ninth month of pregnancy.
mitochondria : Cytoplasmic organelles of characteristic structure containing the enzymes for glycosis and for the citric acid cycle.
mitosis : The series of changes within a cell nucleus by which two genetically identical daughter nuclei are produced.
mixing ratio : The fixed proportions in which two or more substances may become combined, such as the amount of nitrogen in the air compared to the rest of the air. Atmospheric scientists routinely discuss the gas phase concentrations of trace components in mixing ratios expressed in ratios of VOLUMES, as in "the present tropospheric mixing ratio for methane is approximately 1.7 ppmv."
mixing ratio (w) : a measurement of the amount of water vapour in the air of a given sized quantity of dry air; grams of vapour per kilogram of dry air.
Mobile Source :(also call non-point source) consist of emissions from on-road and off-road sources. Cars, light, medium and heavy-duty trucks are considered on-road mobile sources, off-road mobile sources; are tractors, lawn mowers, boats, and airplanes. Although the off road sources usually put out more pollution per hour of work than the on-road, the great number of on-road source put out a larger overall volume into the atmosphere.
molar volume : The molar volume of an ideal gas at 1 atm is 24.06dm3
monotreme : A primitive mammal belonging to the order Monotremata and found only in Australia. They have the reptilian characteristic of a single vent for passing urine, faeces, eggs or sperm. Monotremes lay eggs, suckling their young after these hatch. The only living monotremes are the echidna and the duck-billed platypus.
Moh's scale : a scale of hardness of minerals. The ten standard minerals in the scale, in ascending order of hardness are:
  • talc
  • gypsum
  • calcite
  • fluorite
  • apatite
  • orthoclase feldspar
  • quartz
  • topaz
  • corundum
  • diamond each can be scratched by any of the minerals higher up the scale, and other minerals can be assigned numbers in the same scale, according to which minerals will scratch them.
    mole : a gram molecular mass (also called gram molecular weight) of a substance; the molecular mass of a substance in grams. One mole contains Avogadro's number of particles (6.026 x 1023).
    molecular oxygen : a molecule that is composed of two oxygen atoms, O2, and has no colour, odor, or taste. It is present in both the atmosphere and dissolved in the oceans and freshwater sources exposed to the atmosphere. Solar radiation with wavelengths less then 242 nm can break it back into oxygen atoms, O2 ---> O + O. One of these oxygen radicals in turn can combine with O2 to form ozone, O2 + O ---> O3.
    mollusc : A group of animals, including slugs and snails.
    Monera : The kingdom that includes all those organisms that lack nuclei in their cells; the Monera are all prokaryotes.
    monocotyledon : Any plant having only one cotyledon.
    monocytes : One of three types of leucocytes; large highly mobile cells whose main function is phagocytosis.
    monsoon : heavy winds characterized by a pronounced seasonal change in direction. Winds usually blow from land to sea in the winter, while in the summer, the flow reverses and precipitation is more common. Monsoons are most typical in India and southern Asia.
    Montreal Protocol : A international environmental agreement (one of the first) to prevent the use of substances that are harmful to ozone, such as chlorofluorocarbons and halons, in order to protect the ozone layer in a global manner. It was agreed upon in 1987 and has been amended repeatedly since that time.
    Moon (Astronomy) : The Earth's only natural satellite, having an average distance from the Earth is 238,328 miles and a diameter of 2155 miles. It has no magnetic field and only 1/6th of the Earth's gravity. It's origin is still a mystery with four widely accepted theories; it formed near Earth as a separate body; it was torn from Earth; it formed somewhere else and was captured by our planet's gravity, or it was the result of a collision between Earth and an asteroid about the size of Mars. The last theory has some good support but is far from certain.
    morphine : A narcotic analgesic drug obtained from opium and used in medicine. Its depressant effect on the brain accounts for the pain killing properties. In high doses it also inhibits he breathing and cough centres. Other side effects include constipation, nausea and vomiting. Morphine is an addictive drug and readily leads to severe physical dependence.
    morphogenetic movement : All movements (migrations) that change the shape of differentiating tissues in an embryo.
    mosaic theory : An embryological idea which holds that certain regions of the egg are designated to become specific parts of the organism.
    MTBE : the compound methyl tertiary butyl ether (MTBE) was blended in gasoline originally in 1979 to serve as an oxygenate. This would theoretically cause the combustion process in internally combustion engines to be more complete. This effort to improve air quality by producing a fuel that was more readily oxidized and decrease the resulting troposheric ozone production was somewhat effective. A problem arises, however, in the fact that MTBE moves extremely well in water (it may actually move upstream because of its high affinity for water molecules), causes fish kills due to its toxicity to fish, and even at low concentrations, it can render large surface or groundwater sources to be useless. Its use has since been banned in California.
    mu ( M, m ) :
    Mullein ducts : Tubules that develop in the mammalian embryo just lateral to the Wolffian ducts and are precursors of the Fallopian tubes, uterus, and part of the vagina.
    multiple alleles : Sets of alleles that contain more than two contrasting members for a given locus.
    muon : A negatively charged unstable elementary particle (lifetime 2x10-6 seconds; mass 207 times that of the electron) that decays into an electron and two neutrinos. It has a corresponding antiparticle. It was originally thought to be a meson(and was called the mu-meson) but is now classified as a lepton.
    Murphy's law :
    mutagen : A chemical or physical agent that can cause a change (mutation) in the genetic material of a living cell.
    mutation : An inherited structural or functional variation of an offspring in relation to its parents. Mutations are due to a change in the chemical structure of DNA, the molecule bearing hereditary information. Once a mutation has occurred it is transmitted to future generations.
    mutualism : A relationship between two species of organisms in which both derive benefits from the other. It is more commonly referred to as symbiosis.


    "n" : the photometric parameter generated when calculating a comet's absolute magnitude. It indicates the comet's rate of brightening and fading as it approaches or recedes from the sun, respectively.
    Nacreous Clouds : Clouds that occur in the stratosphere at altitudes above 20 km and are usually iridescent and luminous in color. They may also be called mother of pearl clouds.
    nadir : The pint diametrically opposite to the zenith.
    nalorphine : A specific antidote to morphine overdose.
    nano (n) : 10-9
    naphthalene : a naturally occurring volatile organic compound, is a component of petroleum and coal and is released by the burning of wood or tobacco. It is also used in moth repellants, dyes and pharmaceuticals. Like other nonmethane hydrocarbons, it reacts with NO in the atmosphere to produce NO2. The NO2 is photolized to produce NO and O. The O then reacts with O2 to produce ozone.
    narcotics :
    National Ambient Air Quality Standards (NAAQS) : Sets the levels of air quality for the United States, in the Code of Federal Regulations (40 CFR §50.2), to protect the populationís health. These are the minimum and might be more stringent from state to state.
    National Center for Atmospheric Research (NCAR) : A non-profit organization dedicated to furthering understanding of the Earth's atmosphere. Located in Boulder, Co., NCAR is operated by the University Corporation for Atmospheric Research (UCAR) and sponsored by the National Science Foundation (NSF).
    National Oceanic and Atmospheric Administration (NOAA) : A United States Government agency created in 1970 as part of the United States Department of Commerce to determine how our oceans and atmosphere should be developed, regulated, analyzed, formed, and mined. NOAA tries to achieve these goals with the help of eight major federal services, The National Oceanic Survey, The National Weather Service, The National Fisheries Service, The Environmental Research Laboratories, The Environmental Data Service, The Environmental Satellite Service, The Office of Sea Grant, and The Office of Coastal Zone Management. NOAA has been threatened with extinction in the spring of 1995 with the possible dissolution of the Department of Commerce under the guise of "necessary" budget cuts.
    nebula : A cloud of interstellar gas and dust that becomes visible for one of three reasons. In an emission nebula the gas is ionised by ultraviolet radiation, generally from a hot star within the cloud; the ions interact with free electrons in he cloud, and light (predominantly red and green) is emitted. In a reflection nebula light from a nearby star is reflected in all directions by dust in the cloud, thus illuminating the cloud. The dust in a dark nebula reduces quite considerably the amount of light passing through it (by absorption and scattering) and a dark region is seen against a brighter background.
    nectary : A group of cells secreting nectar.
    negative acceleration phase : The period of decreasing growth rate in a population, following the exponential increase that occurs during the logarithmic phase.
    negative feedback : A mechanism of self regulation where by a change in a system in one direction is converted into a command for a chance in the opposite direction. A means of helping maintain a biological system in dynamic equilibrium.
    Neptune (Astronomy) : The smallest of the gas planets it is the eighth planet from the Sun which it orbits at a distance of 30.06 astronomical units, in an almost circular orbit.. With an equatorial diameter of about 49,400 kilometres (30,700 miles), once every 164.79 years. Neptune is only slightly smaller than Uranus, to which it is a twin planet. One day on Neptune is 16 hours and 7 minutes. The gravity on Neptune is 1.15 of Earth's gravity. It was discovered in 1846 on the basis of predictions made by John Adams and Urbain Le Verrier, but may have been sketched by Galileo in 1613, without him realising it was a planet.
    neural crest : During mammalian embryogenesis, cells that become detached from the forming neural tube, move laterally, and then move dorsally between the closed tube and the overlying ectoderm. The spinal and cranial nerve ganglia are developed from neural crest cells.
    neural tube : In vertebrate embryos the tube formed along the dorsal surface, produced by he infolding of a large mass of ectodermal tissue. The neural tube develops into the entire central nervous system and parts of the peripheral system as well.
    neutrinos : A group of three elementary particles and their antiparticles. They are classified as leptons, have no charge, and are probably massless. One type of neutrino is associated with the electron, one with the muon, and one with the tau particle.
    neutron : An elementary particle that is constituent of all atomic nuclei except 1H. It has no electric charge and its mass is slightly greater than that of the proton. Inside the nucleus the neutron is stable but when free it decays by the weak interaction to a proton, an electron and an antineutrino. It's mean life is about 12 minutes.
    neutron star : A star that has undergone gravitational collapse to the extent that most of the protons making up its constituent atoms have coalesced into neutrons. The density is extremely high (about 1017 kg m-3) and all the pressure exerted by the densely packed neutrons can support the star against further contraction. Neutron stars are thought to form when the mass of the stellar core remaining after a supernova, exceeds about 1.4 sun masses.
    Newton : The SI unit of force defined as the force required to give a mass of one kilogram an acceleration of one metre per second per second.
    nicotine : The only alkaloid (apart from coniie) which is not solid at normal temperatures. Pure nicotine is a pale yellowish oil, but it discolours brown in light. It is present in minute quantities in cigarettes and to a greater extent in horticultural preparations where it is used as an insecticide. Less than one grain can induce a fatal paralysis of the respiratory system, and in addition nicotine can be absorbed through the skin. Large doses produce a burning sensation in the mouth, down through the oesophagus and in the stomach. Vomiting and diarrhoea follow, then mental confusion and giddiness. If the subject is not yet dead then muscular twitching becomes spasmic, and convulsions will be succeeded by unconsciousness and death. Death can occur within a few minutes (Only hydrocyanic acid acts more rapidly).
    niche : The ecological position of an organism - the organisms "occupation" within the biological community.
    nimbo- : indicates a precipitating cloud.
    nimbostratus clouds : Cloud formation consisting of dark-gray layers of clouds and occurring at altitudes which produce prolonged rain and snow.
    nimbus clouds : used to describe a cloud that is precipitating.
    ninhydrin : A substance that reacts with amino acids to produce strongly coloured compounds that can be easily detected.
    nitric acid - HNO3 : this is a corrosive, non-volatile, and inorganic acid. It is a strong acid (dissociates completely in aqueous solution) and is also an oxidizer. In the atmosphere it is formed by the conversion of nitrogen monoxide into nitrogen dioxide, and ultimately into nitric acid:
    2NO + O2 --> 2NO2
    3NO2 + H2O --> 2HNO3 + NO
    Nitrogen monoxide in this process most often come from (fossil fuel-based) combustion processes that use atmospheric air (containing 78.1% N2) which combines with atmospheric oxygen in those high temperature combustion process (see nitrogen monoxide and nitrogen dioxide entries below). Nitric acid is highly water soluble. This solubility with water allows easy removal of nitric acid from the troposphere by atmospheric precipitation. Commonly, this is referred to as acid rain or snow. Nitric acid has a relatively low concentration in the atmosphere but provides an important role in the production of sulfuric acid. It acts as a catalyst in the conversion of sulfur dioxide to sulfuric acid. Sulfuric acid is usually formed within cloud droplets by oxidation of dissolved sulfur dioxide again most foten released by fossil fuel combustion.
    nitrification : The conversion of nitrogen organic compounds to inorganic compounds of nitrogen. This conversion is accomplished, in the main, by bacteria.
    nitrobenzene : nitrogen fixing bacteria : Bacterial organisms that are capable of drawing nitrogen from the atmosphere and converting it into soluble nitrates. These nitrates can then be used by plants.
    nitrogen (N2): a colorless, tasteless, odorless gas which makes up 78.1% of the atmosphere. Atmospheric nitrogen is converted by nitrogen fixation and nitrification into compounds used by plants and animals. In the far upper atmosphere, N2 is broken down when large numbers of energetic secondary electrons are produced and available to react with the N2. This leads to the eventual production of NO in that part of the atmosphere and is not--by definition--anthropogenic in nature.
    nitrogen dioxide (NO2) : is the lesser of the two emitted NOx gases from high temperature combustion in air. It is an important species in the atmosphere. Since it absorbs in the visible wavelength region, creating the Brown Cloud see over Denver, LA, Mexico City, Beijing, etc. and can be photolyzed and yield oxygen atoms that can react with molecular oxygen to create ozone, NO2 and the NO/NO2 ratio is important in tropospheric chemistry.
    nitrogen monoxide (nitric oxide) (NO) : is the principal emitted NOx gas from high temperature combustion in air. This gas can acts a catalyst in the reactions that cause the destruction of ozone. Reacting with ozone and tropospheric radicals, NO is inextricably linked with the polluted urban atmospheric production of NO2, ozone, and other secondary pollutants such as peroxyacetyl nitrate.
    nitrogen oxides (NOx) : produced from high temperature combustion in air. They are nitrogen oxide and nitrogen dioxide.
    nitroglycerine (C3H5(NO3)3) : A yellow oily highly explosive liquid. It is used as an explosive either alone or as dynamite or gelignite.
    nitrous oxide (N2O) : this is a by-product of biological activity of a symbiotic bacteria living in leguminous plant roots. It is a principal greenhouse gas that absorbs in the infrared wavelength region and unfortunately falls in an IR "window" between IR absorbing features of water and carbon dioxide (a characteristic of all the "trace" greenhouse gases with significant radiative forcing). It is also laughing gas used in medicine as a gentle general anesthetic.
    noble gases : The elements forming group 0 of the periodic table. All are odourless, colourless, tasteless gases which are slightly soluble in water. They are virtually inert chemicals owing to their filled outer electron shells ;
    The electronic structures of the noble gasses :
    Inert gas Electronic structure (Bohr model) Electronic structure (s,p,d,f notation)
    Ne 2.8 [He] 2s2 2p6
    Ar 2.8.8[Ne] 3s2 3p6
    Kr [Ar] 3d10 4s2 4p6
    Xe [Kr] 4d10 5s2 5p6
    Rn [Xe] 4f14 5d10 6s2 6p6

    noble metals : Metals, such as gold, silver and platinum that do not rust or tarnish in air or water and are not easily attacked by acids.
    noctulucent clouds : Relatively unusual wavy, thin, bluish-white clouds that form at altitudes of about 80 to 90 km.
    node (botany) : The point where the leaf is attached to a stem.
    "nodoc" : see anticodon.
    nodules : Swellings on the roots of certain leguminous plants where nitrogen-fixing bacteria reside in a symbiotic relationship with the plant.
    nondisjunction : The failure of a pair of chromatids to separate at metaphase, creating an abnormality of chromosome number in both daughter cells. Nondisjunction usually leads to deformed offspring.
    nonmethane hydrocarbons (NMHCs) : These are hydrocarbons such as ethylene, butane, hexane, propane and, by definition, exclude the first member of that analogous series, CH4. Large quantities of NMHCs are emitted from vegetation, the vast majority as isoprene, C5H8. The natural emission of isoprene is significant compared to that of anthropogenic NMHC.
    normal phase HPLC : chromatography in which the stationary phase is polar and the mobile phase is non polar.
    notochord : A rod shaped body located dorsally and serving as an internal skeleton in the embryos of all chordates and in adults of some; replaced by a vertebral column in vertebrates.
    nu ( N, n ) :
    nuclear fission : A process whereby the nucleus divides into two main fragments of nearly comparable mass.
    nuclear membranes : The unit membrane that separates the nuclear material from the surrounding cytoplasm in a cell. The nuclear membrane is not continuous, but rather is broken at different intervals by nuclear pores that provide a physical passage between the nuclear and surrounding cytoplasm.
    nuclear winter : In the event of a significant nuclear war, researchers (Paul Crutzen and John Birks initially) predicted that a barrier of smoke (from incinerated urban centers and forests) would fill tropospheric skies, and eventually surround the earth, reducing the tropospheric temperature and causing damage to ecosystems and atmospheric components such as stratospheric ozone.
    nucleation : A process in which water condenses on a small atmospheric particle. Nucleation aides in the process of condensation (see methanesulfonic acid).
    nucleation scavenging : Term for water vapor that removes particulate matter from the atmosphere.
    nucleic acid : A polymer composed of ribose sugar rings and phosphate groups, with organic bases of thymine, guamine, cytosine, adenine, and/or uracil. Both DNA and RNA are nucleic acids.
    nuclease : An enzyme that hydrolyses nucleic acids by breaking phosphodiester bonds.
    nucleon : A collective name for a proton or neutron.
    nucleolus : nucleoplasm : The living material within the nucleus.
    nucleotide : The molecule formed from the combinations of a purine or pyramidine, an appropriate sugar (ribose or deoxyribose), and a phosphate residue. Nucleotides are the basic units of nucleic acid structure.
    nucleus (atomic): The dense area in the central part of an atom where all the protons and neutrons are located.
    nucleus (cellular): A body found in nearly all cells which contains the hereditary information of the cell and acts as the control centre of the cell function.
    nucleus (astronomical): The actual solid body of a comet. The nucleus is rarely visible when the comet is in the inner solar system because of the coma. It has been referred to as a "dirty snowball" because it is believed to be composed of about 75 percent of various ices and about 25 percent of various dusts. A photo of the nucleus of Halley's comet by the Giotto probe revealed the nucleus as an asteroidal-looking body. Most comet's have a nucleus that measures only a few kilometers across.
    number base : A real number x can be represented using any integer number b as a base (sometimes also called a radix or scale). The choice of a base yields to a representation of numbers known as a number system. In base b, the digits 0, 1, ..., are used (where, by convention, for bases larger than 10, the symbols A, B, C, ...are generally used as symbols representing the decimal numbers 10, 11, 12, ...).


    oblique lighting :
    Occupational Exposure Standard (UK) : The concentration of an airborne substance (averaged over a reference period) at which, according to current knowledge, there is no evidence that it is likely to be injurious to employees if they are exposed by inhalation, day after day. (Specified by HSC in Guidance Note EH40).
    ocean : The oceans cover approximately 70% of the Earth's surface and are apparently unique in the solar system (although keep an eye on some of the giant planets' moons...). The oceans are important for the regulation of tropospheric heat and the storage and production of oxygen and carbon dioxide.
    odour threshold : The minimum concentration of a substance at which the majority of test subjects can detect and identify the substance’s characteristic odor.
    Ogliocene epoch : The third epoch of the Teriary period lasting from about 38 to 24.6 million years ago.
    ohm (W) : Unit of electrical resistance, transmitting a current of one ampere when subjected to a potential difference of one volt.
    oligopeptide : A small number of nucleotides joined by phosphodiester bonds.
    oligotropic (lake) : Lacking in biological productivity; not yielding much biomass.
    omega ( W, w ) :
    omicron ( O, o ) :
    one dimensional model : An atmospheric modelling technique in which a concentration or another unknown can be calculated relative to certain parameters, such as altitude or temperature.
    oogenesis : The process by which haploid female gametes are produced.
    opacity : A measure of light blocking by atmospheric particles. operon, a genetic unit consisting of genes that function co-ordinately under the joint control of an operator and a repressor.
    opium : The dried juice obtained from the seed capsule of the opium poppy. A narcotic drug also used in medicine for pain relief. The main uses today include the extraction of it's active ingredients, morphine, codeine, etc.
    order : A group of genera, all of which agree in some striking particular.
    Ordovocian period : A geological period of the Lower Palaeozoic era. It lasted from about 5.15 to 4.45 x 108 years ago. It is divided into the Upper and Lower Ordovician, based on the graphite fossils that are abundant in the deepwater deposits.
    organ : A unit composed of various types of tissues grouped together to perform a necessary function. The liver and a plant leaf are examples of organs.
    organelle : A small body appearing within the cell cytoplasm, with a characteristic structure and a definite, though perhaps not always clearly defined function. Cytoplasmic organelles include mitochondria, ribosomes, the Golgi complex, and the endoplasmic reticulum.
    orogenesis : The process of mountain building, including folding, faulting and thrusting, resulting from the collision of two continents, which compresses the sediment between them into mountain chains.
    orthochromatic :
    orthogenesis : An erroneous conception, originating in the 19th century, that evolution progresses in a given straight line direction.
    osmium (Os) :
    osmosis : The passage of a solvent from a region of greater concentration to a region of lesser concentration through a semi-permeable membrane.
    ostium : The upper end of the fallopian tubes, where eggs released from the ovaries enter for transport to the uterus.
    outgassing : The release of "young" gases into the earth's atmosphere by volcanic activity.
    ovary : In plants, the basal portion of the pistil which encloses the ovules. The ovules in turn, contain the female sex cell. After fertilisation, the ovary becomes the fleshy part of the fruit and the ovules become the seeds. In animals the organ (usually paired) of the female which produces the ovum, or egg.
    oviparous : Term applied to organisms that lay eggs in which the embryo continues to develop for some period of time, deriving nourishment from the yolk.
    ovoviviparous : Term applied to organisms whose young develop within the body of the mother but derive most or all of their nourishment from the egg yolk.
    ovulation : The release of an unfertilised egg from the ovary. In human beings ovulation involves the discharge of a mature ovum from a Graffian follicle of the ovary.
    ovum : The female reproductive cell containing the haploid number of chromosomes, derived by meiosis from a diploid germ cell. The ovum is fertilised by the sperm, producing the zygote.
    oxalic acid :
    oxidation : A type of chemical reaction involving the loss of electrons. Frequently but by no means necessarily, the element oxygen is involved.
    oxidants : Chemical species that readily accept electrons. The electron accepting species is reduced in a chemical reaction.
    oxidation : a process that results in a species having a higher oxidation state, that is, the net loss of electrons from an atom. Quite often oxygen is involved in the oxidation of another atom therefore it is an oxidant.
    oxidative phosphorylation : The process whereby electrons removed from substrate molecules are passed through the electron transport chain (cytochromes), in such a way that their potential energy is coupled to the formation of ATP (from ADP and inorganic phosphate).
    oxygen (O2) : found on Earth as a gas and constitutes about 20.8% of the air we breathe. Elemental molecular oxygen consists of two oxygen atoms bonded together. A photochemical reaction of oxygen is (ultimately) responsible for the production of ozone in the stratosphere. Oxygen concentrations found in ice core samples (using isotopic 16O/18O rations) have been used to determine past atmospheric levels of oxygen and have helped in determining past climates.
    oxygen debt : The amount of oxygen required to oxidise the excess lactic acid accumulated in muscle cells during strenuous exercise.
    Oxygen Deficiency : Depletion of oxygen content in an atmosphere to below the normal 21%. Exposure to <18% must not be permitted.
    oxygen enrichment : Increase in oxygen content of air to above the normal 21%. Enrichment within a room to >25% can promote or accelerate combustion.
    oxytocin : A hormone produced in the hypothalmus and secreted by the pituitary gland, regulating uterine contractions.
    ozone (O3) : is a molecule that consists of three oxygen atoms bonded together. The ozone layer in the stratosphere absorbs UV radiation and creates a warm layer of air in the stratosphere and is therefore responsible for the thermal structure of the stratosphere. Ozone that is present in the troposphere is mostly a result of anthropogenic pollution and therefore higher concentrations are found in urban areas. Ozone is involved with NOx in the photochemical production of many of the constituents of pollution environments (see nitrogen oxides and hydroxyl radicals.)
    ozone depletion potential(ODP) : The is the ratio of a particular ozone depleting compound environmental effect compared to the depleting ability of a standard compound, CFC-11, which arbitrarily defined as 1.0. An example would be the ODP of of halon-1301 which is about 13.
    ozone destruction : In addition to photolytic destruction by infrared light (wavelengths of 1140 nanometers or less), stratospheric ozone is destroyed by interaction with a variety of chemical substances in the stratosphere. Some of these chemicals, such as the chlorine free radical, liberated by the photolysis of chlorofluorocarbons, are not normally produced there in nature at such high concentrations. This leads to the conclusion that human activities, and not natural chemical cycles, are responsible for the current rate of stratospheric ozone destruction. Ozone destruction is most noticeable (alarmingly!) over the South Pole, where seasonal plummeting in stratospheric ozone concentrations have been measured since the 1970s and are apparently still increasing (1999). That said, estimates based on declining CFC use (because of the Montreal Protocol) suggest that the damage to the global ozone layer will max out soon in the 21st century and that that ozone damage will decrease within the next 75 to 100 years.
    ozone distribution : Nearly all of the planet's natural ozone in the atmosphere is found in the stratosphere. The thickness and distribution of this stratospheric ozone vary seasonally and by location. Ozone also occurs in the troposphere as a pollutant, often in photochemical smog.
    ozone hole : The ozone hole refers to the total amount of ozone in the atmosphere over Antarctica that was discovered to be decreasing at an alarming rate over an observation site in Antarctica. The hole was discovered by J.C. Farman, B.G. Gardiner and J.D. Shanklin.
    ozone formation : Molecular oxygen in the stratosphere is broken into a pair of oxygen radicals by light with a wavelength of 240 nanometers or less. If one of these O radicals encounters an oxygen molecule, it can bond to produce ozone. This reaction is only stable if another molecule is present to absorb the excess energy released as the oxygen radical and molecule bond. This is a called a three body reaction, and the third body exhibits its removal of the excess energy by whizzing off at a higher energy and thereby increasing the temperature of the atmosphere where this reaction occurs.


    Palaeocene epoch : First epoch of the Tertiary period. It lasted from about 65 to 54.9 million years ago. The sudden diversification of the mammals is a noticeable feature of this epoch.
    Palaeozoic era : The era of geological time lasting from about 5.9 to 2.4 x 108 years ago. It is divided into the Upper Palaeozoic which contains the Cambrian, Ordovician, and Silurian periods and the Lower Palaeozoic, containing the Devonian, Carboniferous, and Permian. It is the first era of Phanerozoic time. The Caledonian and Variscan orogenies both occurred in this era.
    panchromatic :
    panicle : Term used when the pedicel are branched, supporting two or more flowers in a loose cluster.
    Pangea : A huge protocontinent thought to have existed 200 million years ago and from which all present continents are thought to have formed.
    paraldehyde : parasite : An organism that derives its food from another species by living in or on the host organism, usually to the detriment of the host.
    parasitism : A type of heterotrophic nutrition found among both plants and animals. An organism engaging parasitism lives in or on the body of a living plant or animal (host) and attains nourishment from it.
    parsec : A unit of distance, used in astronomy, corresponding to a parallax of one second of arc. 1 parsec = 3.26 light years or 3.08 x 1016 metres.
    parthenogenesis : The development of an egg, without fertilisation , into a new individual. Parthenogenesis occurs naturally in some organisms (such as aphids, rotifers, bees and ants) but can be induced artificially in higher forms (such as frogs) by chemical or physical stimulus to the egg.
    partial pressure : The pressure exerted by a given component gas in a mixture of gasses, partial pressure of gas = Volume of gas / total volume
    partial specific volume : The volume increment per gram of solute.
    particle physics : The study of elementary particles and their interactions. Until the discovery of the electron the atom had been thought of as a minute, indivisible "billiard ball". The existence of the electron and the discovery of the proton made it clear that the atom had an internal structure. When the neutron was discovered it appeared that the whole of the universe was constructed of just these three particles. The outstanding problem was the nature of the force that held the neutrons and protons together in the atomic nucleus. The only two fundamental forces known at the time were gravitational force and he electromagnetic force(em);, the gravitational force was too weak to account for the great stability of the nucleus and the em force had no effect on the electrically charged neutron.

    The concept of exchange forces (the meson) and the subsequent discovery of short lived particles led to intensive research into particle physics throughout the world. By the 1960's some 200 elementary particles had been identified and it became clear that there were four basic types of force, in addition to gravitational and em forces there were strong interactions (100 times more powerful than em forces) and weak interactions (1010 times weaker than em forces). It also became evident that some elementary particles were more elemental than others. In general, there are now believed to be two classes, leptons (the electron, muon, tau particle and neutrinos), which interact by the em or weak forces and have no apparent internal structure, and haydrons (including the proton, neutron, pion, etc.), which interact by the strong interaction and do appear to have an internal structure.

    During the past twenty years the main preoccupation of particle physicists has been the elucidation of hadron structure. The current model is concerned with the quark. In this model, haydrons themselves are divided into two classes: baryons, which decay into protons, and mesons, which decay into leptons and photons or into proton pairs. Baryons consist of three quarks and mesons consist of a quark-antiquark pair. Thus all the matter in the universe is now seen as being made of leptons and quarks.

    Quark theory is fairly elaborate; quarks have fractional electronic charges (+2/3 or -1/3 of the electronic charge) and come inn six "flavours" called up (u; +2/3 ), down (d; -1/3 ), charmed (c; +2/3 ), strange (s; -1/3 ), top (t; +2/3 )and bottom (b; -1/3). For each flavour there is an equivalent antiquark (u, d, etc.). The proton consists of uud (2/3 + 2/3 -1/3 = 1) and the neutron consists of udd (2/3 -1/3 -1/3 = 0).

    In this limited form quark theory conflicted with the Pauli exclusion principle and it therefore became necessary to introduce the concept of "colour". Thus each quark can have one of the three colours red, yellow or blue, with the antiquarks having the corresponding anticolours. "Colours" in this sense has no connection with visual colour but the analogy is useful . All haydrons are regarded as white and baryons must consist of a red a blue and a yellow (since these visual colours produce white), mesons consist of a quark of any colour and it's corresponding anticolour. This aspect of particle physics is known as quantum chromodynamics by analogy with quantum electrodynamics.

    Parts Per Million (ppm) and Parts Per Billion (ppb) : These terms give scientists a way to describe how much of a substance is contained in a sample: parts of analyte per million parts of sample, for instance. In atmospheric chemistry these become volume parts of analyte per volume parts of atmosphere: ppmv, ppbv, etc. At low analyte gas phase concentrations the analyte is assumed to act as an ideal gas. For instance, a 1 ppmv concentration of formaldehyde would represent 1 liter of formaldehyde per every 1,000,000 liters of air; also equivalent to 1 microliter of H2CO per 1 L air. In gas phase concentrations these units are also called gas phase mixing ratios. The reason is because they are just that, ratios of analyte volume to sample volume; the volume of the sample doesn't matter.
    pascal (Pa) : Unit of pressure equivalent to one Newton per square metre.
    pathology : The branch of medicine concerned with the study of disease and disease processes in order to understand their causes and nature. The speciality originated in the mid 19th century when Virchow demonstrated that changes in the structure of cells and tissues were related to specific diseases.
    Pauli exclusion principle : In any atomic system no two electrons can have identical wave functions.
    PCV Systems : A PCV system is an air pollution control device in automobile engines. PCV stands for positive crankcase ventilation. Automobile makers began installing PCV systems in all new cars in 1963. It helps to recycle hydrocarbon contaminated gases inside the engine (blowby) back into the engine's combustion process.
    "pecking order" : The establishment of social hierarchies, first noted in domestic chickens.
    pedicel : A flower stalk supporting several flowers without footstalks.
    Pedosphere : This is the area of the Earth comprised of the solid plates of the continental crust, loose rocks and soil.
    penumbra : A partly shaded region round the shadow of an opaque body.
    peptide bond : The bond, formed by dehydration synthesis (elimination of water), which links together two amino acids.
    perennial : Rootstocks that increase and expand yearly.
    perianths : Flowers showing no distinction between calyx and corolla.
    Percutaneous Absorption : Absorption via the skin, e.g. due to local contamination or a splash of chemical.
    Perihelion Date (T) : The date an object reaches its closest distance from the sun.
    Perihelion Distance (q) : The point in an orbit when an object is closest to the sun. The value is usually given in astronomical units.
    Period (astronomical): The amount of time, usually given in years, that it takes an object to orbit the sun.
    periodic table : A tabular arrangement of the elements in order of the atomic numbers, which also brings together those elements who's atoms have a similar pattern of orbiting electrons. Chemically related elements consequently tend to appear in the same column or row of the table.
    Go to table.
    perithecium : bottle-shaped ascocarp with a pore at the top through which individual asci are discharged.
    Permafrost : Soil, silt and rock located in perpetually cold areas which remains frozen year-round. Though a thin layer may thaw during summer months, the majority of the permafrost in a given location will remain frozen until the local climate dramatically changes, as from continental drift toward the equator or global warming.
    permeability : The ability of a material to permit a substance to pass through it. From an actual quantitative level, it is the amount of a substance which passes through the material under given conditions.
    Permian period : The last geological period of the Palaeozoic era, occurring about 3.7 to 2.8 x 108 years ago. Widespread continental conditions prevailed, which continued into the Triassic, and the two periods are often linked together as the Permo-Triassic, during which the New Red Sandstone was laid down.
    Permit-To-Work : A document needed when safeguards provided in normal production are unavailable and the manner in which a job is done is critical to safety. Identifies conditions required for safe operation.
    peroxisome : A cytoplasmic cell organelle containing enzymes for the production and decomposition of hydrogen peroxide.
    Peroxyacetylnitrate (PANs) : A class of chemical substances found as a pollutant in the troposphere, formed by photolysis from natural and manufactured organic chemicals. These chemicals act as irritants and mutagens in mammals and are toxic to many plants.
    persistent train : train luminosity that lasts more than a second.
    perturbation : a disturbance; often develops into a low pressure system.
    peta (P) : 1015
    pH : Symbol for the logarithmic scale, running from 0 to 14, representing the concentration of hydrogen ions or protons (usually hydronium ions) per litre solution. On the pH scale 7 represents neutrality, the lower numbers acidity (acids) and the higher numbers alkalinity (bases).
    pH : The negative logarithm of the hydrogen ion concentration of a solution. It is the quantitative expression of the acidity and alkalinity of a solution and has a scale that ranges from about 0 to 14. pH 7 is neutral; <7 is acidic; and >7 is alkaline.
    phagocyte : A cell in the body capable of engulfing cytoplasm for enzymatic breakdown (phagocytosis). Phagocytes are found in large numbers lining the walls of lymph node sinuses; they destroy bacteria that have entered the body and been picked up by the lymphatic system. Leucocytes and macrophages are examples of phagocytes in man.
    phagocytosis : The engulfing of micro-organisms, other cells, or foreign particles by a cell. For example, phagocytosis occurs when an amoeba engulfs its prey or when a white blood cell engulfs a bacterium.
    pharmacology : The study of the action of drugs on living organisms. Pharmacologists examine the uptake of drugs after administration, the routes by which they reach their site of actin, their subsequent effects, how drugs are destroyed by the body, their unwanted side effects, and the interaction between different drugs. Clinical pharmacology (therapeutics) studies the effects of drugs in treating disease.
    Phenol :
    1) A corrosive poisonous crystalline acidic compound present in coal tar and wood tar that in dilute solutions is used as a disinfectant and
    2) any of various acidic compounds analogous to phenols and regarded as hydroxyl derivatives of aromatic hydrocarbons. When coal and wood are burned for energy, phenols are released into the atmosphere.
    phenotype (genetics): The outward appearance of an organism, as contrasted with its genetic make up (genotype).
    Phi ( F, f ) :
    Protoplasm : The name given to the material of a biological cell.
    phlogiston theory : The theory that held that the substance phlogiston was contained in all combustible bodies and was released from these bodies upon their burning (producing phlogisticated air). It remained popular until the advent of the oxygen theory of combustion.
    phon : A unit used for measuring the loudness of sound equal to the intensity in decibels of a sound of a frequency 1000 hertz which appears to the ear to be as loud as the sound to be measured.
    phosphoglyceric acid (PGA) : An intermediate product in carbohydrate metabolism, composed of a 3-carbon backbone with a phosphate group attached to one (usually position 3) of the carbons.
    phospholipids : An important structural part of the cellular membrane, containing phosphorus, fatty acids, glycerine, and nitrogenous base.
    phosphorylation : The addition of a phosphate group ( such as H2PO3) to a compound, as in oxidative of ADP (producing ATP) during respiration.
    Photic Zone : In the ocean (or in lakes) this is the area near the surface with enough light to support photosynthesis. In this zone, both the chemical and biological activity can be enhanced by penetrating solar radiation. This zone is about 20 meters in depth in the ocean. In the upper surface of this zone, the marine photochemistry is most vigorous. Changes in the ultraviolet light content penetrating this region because of changes in the UV-blocking ability of the ozone layer may create unexpected biological results there.
    Photochemical Smog : Natural and artificially emitted hydrocarbons in the presence of oxides of nitrogen undergo photochemical reactions which produce a cloud of toxic chemicals including ozone and a variety of caustic agents. This process is powered by sunlight and some of the products, such as ozone, reach a peak soon after photon flux from the sun reaches a maximum, around midday. The thermal inversions often associated with some cities can lead to a dangerous buildup of smog in urban areas. Human deaths have been attributed to photochemical smog since the Industrial Revolution in cities such as London and New York.
    photoconductivity : The increase in the conductivity of certain semi-conductors, such as selenium, when exposed to light. It occurs when photons excite electrons in the material form the valence band into the conduction band.
    Photodissociation : This is a specific type of photolysis reaction, in which the destruction of a molecule is initiated strictly by solar energy.
    photoelectric effects : A number of effects in which electromagnetic radiation interacts with matter, frequently with the emission of electrons. These effects include photo conductivity, he photovoltaic effect ad the Compton effect and the Augur effect. The frequency of the radiation (f) has to be such that the energy of the photon , hf (where h is Planck's constant) is sufficient to liberate the electron.
    For solids the minimum energy required is called the work function: for free atoms or molecules it is equal to the first ionisation potential, the effect then being known as photoionization. For most substances, an ultraviolet frequency is needed to eject an electron, but for some metals, such as caesium, visible light is sufficient.
    photoionization : The ionization of an atom when it is bombarded with electromagnetic radiation. The frequency of the radiation has to be such that the energy of its photons exceeds the first ionization potential of the atom.
    Photolysis : The destruction of a molecule by electromagnetic radiation, which provides the energy required for a constituent atom to break the chemical bonds between it and the other atoms comprising the molecule.
    photon : The quantum of electromagnetic radiation, having an energy of hf where h is Planck's constant and f is the frequency of the radiation. It may be regarded as an elementary particle with spin 1 and zero mass that travels at the speed, of light.
    Photostationary State : This describes a condition in which there is equilibrium in a photochemical reaction. For this condition to take place the rate of dissociation of the reactants has to be equal to the rate of their recombination.
    Photosynthesis : a biological process which plays a vital role in cycling the atmosphere's carbon dioxide, while simultaneously producing oxygen and other complex substances. Green plants, with chlorophyll, utilize the sun's energy to convert carbon dioxide and water into the plant biomass while oxygen that is released into the atmosphere.
    photovoltaic effect : The production of a voltage when light falls on certain materials coated with another substance. The effect can be detected by connecting the two materials through an external circuit to generate a current. It occurs in copper (I) oxide on copper and in selenium on iron.
    phrenology : phyletic speciation : The process of evolutionary change in which one population gives rise, over time, to another single population genetically different from the original.
    phylogenetic chart : A diagram showing the evolutionary relationships among a group of species, or with a single species. The so called family tree is an example of a phylogenetic chart.
    phylogeny : The study of the evolutionary history of a species.
    physical environment : All of the elements surrounding an organism but excluding other living organisms.
    physostigmine (ersine) : Extracted by some tribes from the calabar bean and used in ceremonies as an "ordeal" poison. The effects of ingestion are mental excitement and hallucination; an overdose of the drug causes vomiting, epigastric pains, and in severe cases interferes with the function of the heart causing death.
    physiology : phytol : The alcohol constituent of chlorophyll.
    Pi ( P, p ) : In mathematics the value (approx. 3.142 or 22/7 ) that is equivalent to the circumference of a circle divided by it's diameter.
    pico (p) : 10-12
    pilo carpine : an alkaloid extracted from the dried leaves of the jaborandi and used medicinally in eyedrops to constrict the pupil and treat glaucoma.
    Pinhole Camera :

    pinocytosis : The process by which materials can be taken into the interior of a cell without passing through the plasma membrane.
    pion : A group of three elementary particles classified as mesons(p), the charged pions (p+ and p-) and have a mass of 139.6 MeV, the neutral pion (po) a mass of 136MeV. The strong interaction can be represented by the exchange of virtual pions between particles.
    Pirani gauge : A pressure gauge used for measuring low gas pressures. It consists of an electrically heated wire placed into the gas. The rate at which the gas conducts heat away from the wire depends upon it's pressure; the pressure is measured by observing the resistance of the wire at fixed voltage or observing the voltage at a fixed resistance.
    pistil : The seed bearing organ of a flower, consisting of an ovary, style and stigma.
    pistol : A short range small arm that can be used with one hand. There are two classes, the revolver and the automatic.
    placenta : A structure created by the fusion of the chlorion from the young embryo with the wall of the uterus. Respiratory, excretory , and nutritional functions of the foetus are carried on by exchanges across this structure. The placenta also secretes hormones regulating certain aspects of foetal development. Presence of a placenta is characteristic of all mammals, except the marsupials, and monotremes.
    Planck's constant (h): A fundamental constant that relates the quantum of energy (E) of a photon to the frequency (f) of the corresponding electromagnetic radiation by the equation E=hf. It's value is 6.626196 x 10-34 joule second.
    Planck's radiation law : Electromagnetic radiation is emitted from and absorbed by matter in discrete amounts (quanta) known as photons. The energy (E) of a photon is related to the frequency (f) of the radiation by the equation E = hf where h is known as Planck's constant.
    Planck's Law : This is a derived formula, from the German physicist Max Planck, that portrays the amount of radiation emitted by a blackbody as theoretically determined by its temperature. It is an equation that produces a curve, termed Planck's blackbody radiation curve, which illustrates that the warmer a body is, the greater is its blackbody emission at each wavelength and the shorter is the wavelength at which emissions peak.
    planetary motion, laws of :
    The first law states that the planets move around the sun in elliptical paths.
    The second law states that the speed of a planet changes with its distance from the sun.
    The third law states that the sidereal period is related to the cube of the planets distance from the sun.
    Plankton : forms of marine, organic life that gather vital energy for life through photosynthesis. Since they are very low on the food chain, they are vital to all marine life. They are also vital to the atmosphere in that they consume large amounts of carbon dioxide, which contribute to enhanced global warming when excess amounts are present. Plankton are considered to be one of the more important contributors of oxygen to the atmosphere.
    plasma (biology) : A protein containing fluid, the liquid portion of blood.
    plasma (physics) : A gas, the atoms of which have been completely ionised. Sometimes called the fourth state of matter, plasmas occur at enormously high temperatures, such as those in the Sun. Plasmas are also created in thermonuclear reactors.
    plasmagene : A term applied to a gene of cytoplasmic, rather than nuclear origin.
    plasma membrane : A lipoprotein of a definite structure which surrounds and contains the living matter within a cell. The membrane has three layers: two outer protein surfaces surrounding an inner core of lipid. The polar part of each lipid molecule is associated with protein on the surface, while the non polar portions into the middle of the "sandwich". The average plasma membrane has a diameter of 75 angstroms.
    plastic : any synthetic organic polymer that is liquid at some stage in its manufacture. Plastics are classified by their behaviour on heating. Thermoplastics soften on heating and harden as they cool, for example polystyrene and polyvinyl chloride. Thermosetting plastics remain rigid in their final shape and do not soften on heating, for example resins, melamine, polyester, Bakelite.
    During manufacture plastics are moulded and shaped while they are in the heat softening stage and then cooled for thermoplastics, or heated further for thermosetting plastics to yield the final product. The processing of plastics can produce a wide variety of materials from rigid and inflexible to soft and bendy. They can be extruded to make pipes and rods. Plastics can be strengthened by the addition of carbon fibres for use in aircraft or engineering.
    Due to the difficulties in disposal of plastics a number of biodegradable plastics are now in use, including polyhydroxybutrate (PHB), which is made from sugar and digested by micro-organisms in the soil.
    plastic (adj.) : describing a material or process in which the material is deformed by a force and does not return to its original shape once the forced is removed.
    plastids : Small bodies occurring in the cytoplasmic portion of plant cells. They are classified according to colour.
    Plate Tectonics : The process of planetary surface plate formation, movement, interaction, and destruction. The consequence of this process is that many regions of the planet are situated near interacting--and slowly moving--plates. The process causes earthquakes such as those along the West Coast of the United States.
    plate tectonics : The theory developed mainly in the 1960's that the Earth's crust is divided up into rigid plates (oceanic, continental, or a combination of both), which move about the Earth's surface at rates between 10 and 90 mm per annum. The edges of the plates are called margins. At constructive plate margins new oceanic crust is created where two plates are moving apart and magma rises to fill the gap; this occurs at mid ocean ridges. At destructive plate margins two plates collide and one dips beneath the other, producing deep sea trenches and the associated volcanic land arcs. Where two continental plates collide, mountain chains are formed. All the major structural features of the Earth's surface and almost all seismic and volcanic activity can be ascribed to plate movements.
    platinum (Pt) : a very unreactive metal used to make inactive electrodes for electrolysis. It also acts as a catalyst in a wide range of reactions. at. # relative at. mass m. p. b. p. relative density 78 195.1 1 772 oC 3 800oC 21.3
    platonic solid : any of the five regular polyhedrons - the cube, dodecahedron, icosahedron, octahedron, tetrahedron.
    Pleistocene : The period of geological time that lasted from about 1.8million to 100,000 years ago. It is often called the Ice Age because during this time the earth experienced great fluctuations in temperature: cold glacial periods, when the ice margins advanced towards the equator, separated by warmer interglacials, when temperatures at times were higher than today. Four main ice advances are recognised in the Pleistocene. Fossils from the Pleistocene include horses pigs and elephants.
    Pleistocene : An epoch in Earth history from about 2-5 million years to 10,000 years ago. Also refers to the rocks and sediment deposited in that epoch.
    Pliocene epoch : The final epoch of the Tertiary period lasting from about 5.1 to 2 million years ago. I t was a time when world temperatures were falling and many species of mammals that had flourished earlier in the Tertiary were becoming extinct.
    Plume : a visible smoke-like structure, which may contain pollutants emitted from an exhaust or smoke stack and released into the atmosphere. This elongated band of smoke has changing characteristics that vary with its local environmental conditions. These conditions may include the physical and chemical nature of the pollutant, weather conditions and downwind topography.
    Pluto (Astronomy) : The ninth planet from the Sun and the smallest of the known planets, orbiting at an average of 39.44 astronomical units every 248 years. The orbit is highly elliptical, the distance varies between about 30 and 50 AU at different parts of its orbit, which takes it inside the orbit of Neptune for approximately 20 years. It has a diameter of 2,170 miles and a surface gravity equivalent to 0.05 of Earth's gravity The surface temperature is -369o F. One day on Pluto equals 6 Earth days, 9 hours, and 18 minutes. Pluto's orbit is also highly inclined, tilted 17 degrees to the orbital plane of the other planets.
    It has been suggested by some that the irregular orbit of Pluto is due to another planet in our system that has not yet been discovered.
    pnicogens : The group five elements.
    Point Source : Pollutants which are put into the atmosphere by stationary objects, such as refineries, power plants, mills, and the like. In Texas any source that emits more than one ton in a calendar year is considered a point source.
    polar body : The small daughter cells produced during meiotic divisions of the oocyte. From the first division one polar body is produced; form the second three polar bodies are produced. A single primary oocyte thus gives rise to one large mature ovum and three polar bodies. The polar bodies contain the extra sets of chromosomes produced by meiosis. They contain very little cytoplasm however, since most of this is reserved for inclusion in the single ovum.
    polarisation : The term applied to the unequal distribution (separation) of charged ions, producing an electric potential. Cell membranes are said to be in a state of polarisation when they have a greater concentration of positive ions on the outside than on the inside, or vice versa.
    Polaroid Camera : Historically used by the Police when image sharpness is not important. As these provide an instant print there is no chain of custody.
    Polar Stratospheric Clouds (PSCs) : stratospheric clouds.
    Polar Vortex : This is a phenomenon that occurs during the polar winter in which stratospheric air moves in a circular motion, with an area of relatively still air in its center. The temperature in the vortex is approximately -130oF (-80oC), which assists in the formation of polar stratospheric clouds. Though usually more prolonged and colder over Antarctica, the Arctic polar vortex does form to a degree, and when the temperatures there are coldest and the vortex persists, Arctic stratospheric ozone destruction on Arctic polar stratospheric clouds has also been observed.
    Pollutants : any substance, usually an unwanted by-product or waste, that is released into the environment as a result of (human) activities that alter the chemical, physical and biological characteristics of the environment. These substances may be found in any of the solid, liquid or gas phases. Their long-term effects are difficult to predict and depend upon future human or cultural judgments.
    polydactyly : Supernumerary fingers which, although normally existing as merely an ill-formed appendage to the thumb or little finger, can occasionally manifest as six or more fully formed fingers.
    polygenic character : A quantitatively variable phenotypic trait determined by interaction of numerous genes.
    polymorphism : The existence within a single species of members showing many different, but distinct and recurring forms; for example, the drone, queen and workers, occurring in the honeybee.
    Polynuclear Aromatic Hydrocarbons (PAHs) : These compounds are large ring aromatic hydrocarbons that are molecules containing carbon and hydrogen. It could also be any large ring that consists of five or more cyclic compounds of carbons and any elements that may be bonded to the ring. They usually exist in nature in low amounts. Many times these hydrocarbons exist within the atmosphere in the aerosol phase from combustion processes.
    polyribosome : A cluster of connected ribosomes, usually arranged along a strand of mRNA.
    polysaccharides : Complex carbohydrate molecules built up from simpler sugar units (such as glucose) into long chain polymers. Polysaccharides are the major constituents of the cell walls and capsules of various micro-organisms.
    polysome : A cluster of connected ribosomes, usually arranged along a strand of mRNA.
    polyspermy : The fertilisation of an egg by more than one sperm at a time.
    population genetics : The application of genetic principles to a large number of breeding organisms.
    Position Angle (PA) : An angular measurement indicating which side of the comet nucleus something is located. A "PA" of 0 degrees indicates an object is located north of the nucleus, while 90 degrees indicates east, 180 degrees is south, and 270 degrees is west. It is most commonly used to indicate the direction the tail is pointing. On occasion, when a comet's nucleus has broke up, the position angle is used to indicate which direction the nuclear fragments are located from the primary nucleus.
    positive acceleration phase : The first section of a sigmoid growth curve for a population, where the system described is just beginning to increase.
    positive feedback (biology) : An abnormal state in which a change in a systemin one direction serves as a command for continued change in that same direction. This can create a severe physiological imbalance leading to the death of an organism.
    positron : The antiparticle of the electron, having the same mass and spin as the electron but opposite electric charge. A positron and an electron annihilate each other on collision, producing two gamma - ray photons.
    potential energy : Energy capable of doing work.
    Practicable : Capable of being done in the light of current knowledge and invention.
    praseodymium (Pr) : Pre-Cambrian : Geological time from the formation of the Earth's crust, about 45 to about 5.9 years x 108 years ago when the Palaeozoic era began. Pre-Cambrian rocks lie below the Cambrian system and fossils are rare and often obscure. The rocks have been subjected to much alteration because of their great age. Most are metamorphosed and have undergone one or more Pre-Cambrian mountain building periods as well as later ones. The largest areas of exposed Pre-Cambrian rocks are the shield areas. Correlation of successive strata is done, where possible by radioactive dating.
    Precambrian : All geologic time from the beginning of Earth history to 570 million years ago. Also refers to the rocks that formed in that epoch.
    precipitate : An insoluble product of a chemical reaction in a solution.
    Precipitation : What often occurs when clouds form upon reaching 100% relative humidity. If condensation nuclei are present, liquid or solid particles of water will form. When this material becomes heavy enough to fall towards the ground, it is known as the common phenomenon snow, rain, sleet, or hail
    precision : the scatter of repeated measurements, i.e. if measurements on the same sample are close to each other then the method is said to give precise results.
    predation : The process by which one species uses another species for food.
    preformation : The idea that an already formed, miniature individual exists within the egg and merely increases in size during embryological development. primary feathers, The main flight feathers, on the outer part of the wings. primary germ layers, The first distinguishable areas within the developing embryo, namely the ectoderm, mesoderm, and endoderm. These areas give rise to the tissues and the organs of the mature organism.
    Primary Pollutant : This refers to the types of pollutants that are either found in the atmosphere or on the ground and are emitted directly from some sources such as automobile tailpipes or smoke stacks. This is contrasted with secondary pollutants which in and of themselves are not directly emitted from a source. Instead they are created from chemical and photochemical reactions of primary pollutants. Nitrogen monoxide is an example of a primary pollutant and ozone is an example of a secondary pollutant.
    primary spermatocyte : The cells in the testes that derive from spermatagonia and ultimately undergo meiosis to produce haploid sperm.
    primary standard : A substance that is used to make a primary standard by dissolving in deionised water. They must be
    i. chemically stable in the solid and aqueous states,
    ii. pure (at least 95%), and
    iii. soluble in water.
    primitive streak : A longitudinal groove that develops on the surface of the embryo of fishes, reptiles, birds and mammals. Formation of the streak is a consequence of the movement of cells and

    Pulmonary Oedema : Production of watery fluid in the lungs.
    Pyrophoric Substance : A material that undergoes such vigorous oxidation or hydrolysis (often with evolution of highly flammable gases) when exposed to atmospheric oxygen or to water, that it rapidly ignites without an external source of ignition. This is a special case of spontaneous combustion.


    Q-fever : An infection with the organism Coxiella burnetti. It affects mainly cattle and sheep but can be transmitted to humans through contaminated milk. The incubation period is two to four weeks and the disease usually takes the form of a viral pneumonia. Treatment is with tetrcycline antibiotics.
    Qualitative data : That which can be placed in categories or with respect to attributes.
    quantasome : One of the individual membranous structures arranged in columns within a granum. Molecules of chlorophyll are aligned on the quantasomes.
    quantitative : That which can be measured or described in some definite and precise (generally numerical) form.
    quantum : A tiny energy packet in which light travels.
    quantum number : An integral or half integral number that gives the possible values of a property of a system according to the quantum theory. For example, in Bohr's atomic theory the angular momentum of an electron moving around an atomic nucleus can only have the values nh/2p, where n is a quantum number specifying these values and h is Planck's constant. Bohr's theory has now been replaced by the more versatile theory of wave mechanics, but the concept of quantum numbers is useful in some contexts. It is also used to quantify the properties of elementary particles. For example spin is characterised by the quantum numbers +1/2 or -1/2 for an electron, depending on whether it is parallel or anti-parallel to a specific direction. Parity, electric charge, strangeness, charm, isotropic spin, etc. are other properties of elementary particles expressed by quantum numbers.
    quantum theory : The model which holds that light is composed of tiny energy packets (quanta, or photons) which are given off by any light emitter and travel intact through space.
    quarantine : The period during which a person or animal suspected of carrying a n infectious disease is kept in isolation. The term was originally applied to a 40 day period but is now slightly longer than the incubation period of the disease.
    quark : Any of a group of hypothetical components. Quarks are held to carry a charge one third or two thirds of that of the proton. quark theory, The recapitulation, at a deeper level, of efforts earlier in the century to explain all atomic properties in terms of electrons, protons and neutrons.
    quasar : A class of celestial objects lying beyond our Galaxy. They appear as star-like points of light, each emitting more energy than several hundred giant galaxies. Quasar redshifts are extremely large, indicating that they are the most distant and the youngest extragalactic objects known. They must be highly luminous to be visible at such distances. Of the 3500 quasars known, the most distant is 73x1027 miles away. They appear to be about 0.01 x the size of the stars of the Milky way but which radiate between 50 and 150 times as much energy.
    Quasi-Biennial Oscillation : Periodic variation in the direction, either easterly or westerly, of tropical lower stratospheric winds. The direction changes every 26 months.
    Quaternary : The period of Earth's history from about 2 million years ago to the present; also, the rocks and deposits of that age.
    Quaternary period : The most recent period of geological time which includes the Pleistocene (Ice age) and Holocene epochs. It is the period in which man became the dominant terrestrial species. Some authorities consider the Quaternary to be a division of the Tertiary.
    quinine : A bitter drug obtained from the bark of the cinchona tree, used to reduce fever and as a tonic. It was the first drug used to treat Malaria but has now been largely replaced by other drugs which have fewer side affects and which are less toxic.
    quinidine : A quinine like compound used to treat abnormal heart rhythms.
    quinone (O:C6H4:O): An aromatic compound with two hydrogen atoms in the benzene ring replaced by two oxygen atoms. Quinones are used in photography and dye manufacture and are found in plants.
    quotient : The result of a division sum.


    r- strategists :
    raceme : Flowers arranged like a spike, but with footstalks.
    rad : The unit of absorbed dose on ionising radiation equivalent to an energy absorption of 100 ergs per gram of irradiated material.
    radial velocity : The velocity of a star etc. along the line of sight, i.e. towards or away from the earth. It is calculated from the Doppler shift on the lines of the stars spectrum.
    radian : The SI unit of plane angle equal to the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle, i.e. 1 rad = q(p/180).
    Radiant : The point from which a meteor appears to emanate.
    Radiant Drift : The movement of a meteor shower's radiant against the star background. This characteristic is common to all meteor showers and is caused by Earth's passage through a meteor stream.
    Radiation Flux : This is defined as the way heat from the sun is absorbed, scattered, returned, or deposited around the earth and can be expressed as some radiation arrival rate per the unit of area of the surface. The radiation flux can be the total amount of radiation that the earth collects, emits, and disperses.
    Radiative Forcing : Reduction of radiation reflecting from earth per units of increase of a chemical component that causes this change in the atmosphere. The result is often used to compare the relative effect of greenhouse gases which can alter climate on earth. This means that components that are present in the atmosphere at low concentrations (e.g. methane at 1.7 ppmv) but with high radiative forcing have a greater effect on global warming than higher concentration components with a lower radiative forcing.
    Radical (free radical) : A highly reactive molecule or atom with an unpaired electron. The species is often represented by a formula with a single dot as the unpaired electron.
    Radical Chain Reaction : Free radicals are molecules that, through photolysis or chemical reaction, have an unpaired electron in their outer valance shell. These radicals are very reactive and thus have a short life. When a free radical reacts with a more stable molecule, the radical often pulls an atom from it and becomes a stable molecule itself. The original molecule then becomes a free radical and will react with other species of atoms and molecules in a long series (or chain) of reactions until the process reaches the termination phase. In this phase two free radicals combine, sharing the pair of electrons and breaking the chain.
    Radical Propagation : Free radicals react with molecules, atoms, other radicals in long series of chain reactions. A radical is formed in the atmosphere through photolysis or chemical reaction. Radicals are very reactive and will pull atoms or electrons from other molecules to fill their outer valance shell. New radicals may formed from the original molecule which then react with another molecule, etc. This reaction propagates from one species to another until a termination reaction occurs. The termination reaction usually involves the reaction of two free radicals to form a stable product. Radioactive Decay - The spontaneous breakdown of certain kinds of atomic nuclei into one or more nuclei of different elements, involving the release of energy and subatomic particles.
    radioactive decay : The decrease in mass of certain unstable elements by emission of elementary particles, continuing until a stable isotopic form has been reached.
    Radiocarbon Dating : Establishing the relative age of various materials with the use of carbon -14. This involves measuring the amount of 14C and of 12C and comparing the measured ratio to the one established by the production of 14C in the upper atmosphere by cosmic rays. When an organism is alive the 14C : 12C ratio in its biomass is constant (because of constant atmospheric 14C production, difussion to the lower atmsophere, absorption by organisms, and because of constant 14C radioactive decay) but when the organism dies the ratio begins to change, at a very predictable rate. Therefore knowing the carbon -14 : carbon -12 ratio now in some artifact gives a very good measure of how long the carbon has been "dead." The object however must obviously have organic material either in it or on it for this method to work. Also the lenth of time one can "look back" is limited because the amount of carbon -14 must be detected with some certainty for the age to be known with confidence, and the longer the sample has been dead the less 14C is present because it is continually decaying.
    radio galaxy : A radio source that lies beyond our Galaxy, is identified with an optical galaxy, and the radio-power output of which greatly exceeds that of a normal galaxy. The size can be immense. A massive black hole at the galaxy centre has been postulated as a possible energy source.
    radiography : The technique of examining the internal structure by passing X-rays or gamma radiation through it to produce an image on a photographic plate or fluorescent screen. Radiography is used in medicine and in industry to find structural defects.
    radiosonde : a light-weight instrument package carried aloft by a weather balloon; radios to earth upper atmosphere data.
    Rainout : One item necessary for a rain drop to form is called a condensation nucleus. Pollutants in the air such as nitric acid and sulfuric acid form nucleation sites (particles) where water vapor often condenses and forms a droplet. As these droplets grow they collect more moisture and may ultimately fall out as precipitation. This accounts for some of the acid rain deposition on the planet's surface.
    random errors : these result in repeat measurements on the same sample to vary in a number of tests.
    rangefinder : a camera in which the subject is viewed through a separate view finder. There will always be the problem that what you see may not be what is taken, the classic examples being close ups of blurred fingers, and lens caps left on.
    Raoult's law : The partial vapour pressure of any volatile component, A, of an ideal solution is equal to he vapour pressure of pure A multiplied by the mole fraction of A in the solution.
    Rayleigh Scattering : The scattering of light by a body with a particle diameter (Dp) less than 0.03 micrometers is termed Rayleigh Scattering. The wavelength of light scattered is dependent on the Dp, and the amount of light scattered is dependent on the number of particles present per unit volume. Shorter visible wavelengths, such as blue, are scattered by smaller particles than are the longer wavelengths like red.
    Reaction Rate : The speed of chemical reactions is expressed as a rate of change in the concentration of a participating species with respect to time.
    Reasonably Practicable : The implication that the quantum of risk is balanced against the sacrifice or cost in terms of money, time and trouble necessary to avert that risk. If the risk overweighs the sacrifice or cost, additional precautions are necessary.
    recessive (genetics) : referring to the relative lack of phenotypic effect of a gene in the presence of its dominant allele. Thus the gene for the blue eyes is said to be recessive for that for brown in the human population, because when one allele for blue eyes and one for brown eyes are present in an individual, the blue condition is masked and the individual has brown eyes. recombination (genetics), The formation of new genotypes (a combination of genes not present in either of the parents) in offspring due to independent assortment of genes and chromosomes during gamete formation.
    red giant : A greatly distended cool but very luminous giant star, often variable in nature. It is one of the final evolutionary stages of a normal star, attained when its central hydrogen has been converted to helium. Hydrogen burning in a shell surrounding the inert helium core causes a rapid expansion and cooling of the outer atmosphere of the star.
    red shift : An overall displacement towards larger wavelengths of the spectral lines of a celestial object. Its astronomical significance, suggested by Hubbell, is connected with it's use as the basis of the theory that the universe is expanding. A red shift usually arises from the Doppler effect, that is from recession of a celestial object. It increases as the objects radial velocity increases and for an extragalactic body can be used as a measure of distance. A gravitational redshift occurs whenever radiation is emitted by a body: it is generally negligible except when the gravitational field is very strong.
    reduction (chemistry) : A reaction involving the gain of electrons.
    reduction division : A cell division, during which the number of chromosomes in each daughter cell is reduced to one half of that found in the parent cell. This is accomplished by nuclear division without previous chromosomal division.
    refraction : The bending of a beam of radiation as it passes from one medium to another. For a light ray the amount by which it is bent depends on the angle of the incident ray and on the refractive indices of the two media, the exact dependence being given by Snell's law. Refraction is caused by the difference in the velocity of the radiation of the two media. The ratio of the velocity of light in the media is known as the refractive index. If the first medium is a vacuum, the ratio is known as the absolute refractive index.
    regeneration : The development process by which a lost part of an organism (such as an organ, part of an organ, or tissue) is replaced after damage. Repair of wounds and the regrowth of a salamanders amputated arm are examples of regeneration.
    relative density (specific gravity): The density of a substance divided by the density of water at 4oC. This value is numerically one thousandth of the density.
    Relative Humidity : This is the ratio between the actual water vapor content of the atmosphere and the maximum water vapor content possible at that given temperature. If the temperature of a given parcel of air rises, the amount of moisture it can hold increases and as such its relative humidity decreases. If there is no change in temperature but the moisture content decreases then the relative humidity will again decrease because the ratio of actual water vapor present is less than the maximum amount the air could hold. Conversely, if the water content does not change but the temperature falls, the relative humidity increases until saturation and possible precipitation occurs.
    relative humidity : a ratio of the amount of water vapour that the air is holding to the amount of water vapour the air can hold, which depends on temperature.
    relative velocity : The velocity of one body relative to another.
    Reportable Disease (UK) : A disease which must be reported to the authorities when linked to specified types of work. (The Reporting of Injuries Disease and Dangerous Occurrences Regulations 1985).
    Respirable Dust : That fraction of total inhalable dust which penetrates to the gas exchange region of the lung.
    respiratory assembly : A series of complex molecules (including cytochromes), found on the inner membranes of mitochondria, and capable of oxidation and reduction. Such assemblies accept electrons from reduced acceptors during the citric acid cycle and pass them along to the final acceptor, oxygen. The enzymes for oxidative phosphorylation are also components of the respiratory assembly.
    Respiratory Sensitizer : A substance that may cause sensitization on inhalation, causing, e.g., asthma, rhinitis or extrinsic allergic alveolitis.
    response : A change in behaviour on the part of an organism (or tissue) as a result of some chemical or physical change in the environment.
    restriction fragment length polymorphism : a technique, also known as DNA fingerprinting, that allows familial relationships to be established by comparing the characteristic polymorphic patterns that are obtained when certain regions of genomic DNA are amplified (typically by PCR) and cut with certain restriction enzymes. In principle, an individual can be identified unambiguously by RFLP (hence the use of RFLP in forensic analysis of blood, hair or semen). Similarly, if a polymorphism can be identified close to the locus of a genetic defect, it provides a valuable marker for tracing the inheritance of the defect.
    Return Stroke : A short-lived, high amplitude discharge of electricity that accompanies a cloud-to-ground lightning event. The bright lightning flash that is visible to the human eye is actually composed of extremely rapid electric discharges called strokes. The return stoke follows a downward extending leader, or conductive path of ionized air. The electrons in the cloud flow down this conductive pathway toward the surface of the earth. As electrons continually migrate down the path, electrons remaining higher up on the path in the cloud begin to consecutively move down the channel to the surface. Since the path of electron flow is progressively lengthened upward, the discharge of the elevated electrons high in the cloud to a lower place in the cloud and then down the pathway to the ground is called the return stroke.
    reverse phase HPLC : chromatography in which the stationary phase is non-polar and the mobile phase is polar.
    reversible reaction : A reaction system where reactants and products are inter convertible. If left to themselves , reversible chemical reactions reach an equilibrium point where just as much reactant is being converted into product as product into reactant at any time. Nearly all chemical reactions are to some extent reversible.
    revolver : A short range small arm having a revolving cylinder containing the rounds behind the barrel. In single action types pressing the trigger cocks the weapon and simultaneously rotates the cylinder; further pressure fires it. Double action types perform these functions automatically but their stiffer mechanism impairs accuracy. Calibre's range from .21 inches to .455 inches.
    Reynolds number :
    Rhesus (Rh) factor : An antigen found in the red blood cells of certain human beings (designated Rh+). The Rh factor acts as an antigen so that individuals with this factor cannot donate blood to individuals who normally lack it (Rh- individuals). The factor derives its name as it was first discovered in the Rhesus monkey.
    rho ( R, r ):
    ribonuclectic acid (RNA) : A complex single stranded molecule consisting of repeating nucleotide bases; adenine, guanine, cytosine and uracil. At least three types of RNA are known, all of which are involved in transcribing the genetic code into protein.
    ribosomal RNA (rRNA): A type of RNA found as part of the ribosomes. The function of rRNA is not well understood although it appears to have some role in protein synthesis.
    ribosomes : Small particles found either free in the cytoplasm or attached to the outer surface of the endoplasmic reticulum in the cells of all eukaryotes and many prokaryotes. Ribosomes contain high concentrations of ribonucleic acid (RNA) and are centres of protein synthesis.
    ricin poisoning :
    Richter scale : A logarithmic scale (from 0-9) used to measure earthquake magnitude. It is based on seismic recordings and takes into account the distance from the epi-centre. The strongest earthquake so far recorded had a Richter scale value of 8.6
    ridge : an area of high pressure. An area of anticyclonically curving winds.
    rifle : A shoulder small arm with a spiral inside its long barrel to make the projectile spin during it's trajectory.
    rifling marks : The marks formed on a bullet as a result of its passage along the barrel of a firearm. Revolvers and self loading pistols are divided into five "types":

    Steer type Used in all of the earlier self loading pistols
    Browning type The most common with six broad grooves with narrow lands and a right hand twist.
    Colt type Used in all Colt pistols, Bayard pistols and Spanish copies of the Colt. Six broad grooves with narrow lands and a left hand twist.
    Webley type Used in all Webley revolvers. Seven broad grooves with narrow bands and a right hand twist.
    Smith and Wesson type Used in all S+W revolvers, Harington and Richardson revolvers and Iver Johnson revolvers but not used in any self loaders. Five grooves and lands of equal width with a right hand twist

    Right Ascension : The celestial equivalent of Earth's longitude, beginning at a line running pole to pole and cutting through eastern Pegasus. In meteor astronomy the right ascension is handled in degrees, starting at zero degrees and advancing eastward around the sky for a full 360 degrees ending in eastern Pegasus. For the rest of astronomy, the right ascension is handled as a time measurement. Since it takes 24 hours for the Earth to rotate, the sky is divided into 24 one hour wide bands. Each hour of right ascension equals 15 degrees.
    roentgen : A unit used to measure the amount of energy in X-ray (or gamma ray) beams. One roentgen is the amount of radiation which, under ideal conditions (0oC and 760Hg), liberates 2.083 x 109 ion pairs per cubic centimetre of air.
    rootstock : An underground stem.
    RR Lyrae stars : A class of short period pulsating variable stars that are very old giant stars found principally in globular star clusters, all with about the same mean luminosity.
    rudimentary phallus : Genital folds in both male and female embryos. In males the rudimentary phallus develops into the penis. In females the phallus grows only slightly and develops into the clitoris.
    Rydberg constant : 1.097 x 105 cm-1.


    safe system of work : A formal procedure resulting from systematic examination of a task to identify all the hazards. Defines safe methods to ensure that hazards are eliminated or risks controlled.
    satellite : can be natural or artificial. The artificial are electronic devices placed into orbit to monitor and examine regions which we may not be able observe from earth. These are used routinely to monitor atmospheric ozone, ultraviolet radiation, and many other constituents. Satellite altimetry and radar interferometry are used to measure magnetic field intensity and track Antarctic ice flow.
    saturated hydrocarbons : a hydrocarbon in which the maximum valencies of the carbon atoms are satisfied by single links.
    saturation : the point at which the air cannot hold any more water vapour; the point at which condensation occurs. RH =100%. Saturation is where the amount of water condensing is equal to the amount of water evaporating.
    Saturn (Astronomy): The sixth planet from the sun with an orbit of 29,48 Earth years, and a spin period of 10 hours, 39 minutes and 20 seconds. It has a diameter of 74,400 miles (the second largest of the planets) and a gravity equivalent to 1.07 that of the Earth. It has 21 moons and over a thousand rings. It is the least dense planet in the solar system and has no solid surface. A magnetic field was discovered around Saturn, aligned parallel to the planet's rotation axis.
    scalar quantity : A quantity that is represented by magnitude only. Unlike a vector quantity a scalar quantity has no direction. Examples include mass, time and speed.
    Schlieren photography : A method of observing differences of density in a transparent medium, such as air. Light from a spark is photographed as it passes through the medium; any differences in density present cause local variations in the refractive index, which show up as streaks in the photograph. The method is used for observing sound waves, shock waves and flaws in glass.
    Schwartzchild radius (SR) : The radius of a contracting star at which nothing, including light, can escape from it. It then becomes a black hole. The Schwartzchild radius for the Sun is 3 km (actual radius 7x108 m).
    sclerotium (pl. sclerotia) : firm mass of hyphae, usually without spores, which can survive dormancy and give rise to mycelia or a fruiting body. Usually visible with the unaided eye.
    scopolamine :
    Scott test : A three part test for cocaine. Solution A is composed of 2% cobalt thiocyanate in one part each of water and glycerine. This is added to the suspect substance which, if it contains cocaine, will turn it blue. Confirmation can be provided by solution B which is concentrated hydrochloric acid, and which will turn the blue solution pink. With the addition of solution C, chloroform, the blue colour will reappear in the chloroform layer.
    sea level : This is the average level of the ocean over the entire earth. Tidal fluctuation is taken into account when determining sea level. Mean Sea Level (MSL) is used to reference the height of structures above ground level and depth below the ocean's surface. Atmospheric pressure is also referenced from sea level. At sea level, 760mm (29.92 inches) of mercury is normally displaced by the pressure of the air column above that point on the earth.
    secondary spermocyte : The daughter cells produced by the first meiotic division if the primary spermocyte during spermatogenesis.
    secretin : hormone secreted by the cells of the duodenum under the stimulus of hydrochloric acid from the stomach. Secretin in turn causes the pancreas to secrete certain digestive enzymes into the duodenum.
    sediment : Particles carried by water or air that are deposited in other areas or elevation are called sediment. Usually associated with water flow, sediment will accumulate at the mouth of a river or stream as it empties into a larger, slower moving body of water. Sediment deposition is also effected by particle size.
    sedimentary rock :
    seismic belts : The narrow distinct belts on the Earth's surface that are subject to frequent earthquakes. They usually follow the line of plate boundaries, especially along mid-ocean ridges, near young orogenic belts, along island arc systems, and along major faults.
    seismology :
    segregation (of alleles) : The separation during gametogenesis of paired factors influencing a single condition.
    selectivity : the extent to which a method suffers from interference.
    seminal vesicles : the portion of the male reproductive duct in which sperm are stored prior to copulation.
    seminiferous tubules : Tubules within the testes where the male sperm are produced. Each testis contains about 1000 highly coiled seminiferous tubules.
    semi-permeable (differentially permeable): Term applied to a membrane that allows some substances to pass through while prohibiting the passage of others.
    sensitization dermatitis : Inflammation of the skin due to an allergic reaction to a sensitizer .
    sex chromosome : The chromosomes commonly referred to as "x" and "y", whose presence in certain combinations determines the sex of an organism.
    sensitivity : the ability of an instrumental method to distinguish between small differences between analyte concentrations.
    sessile : Leaves or flowers connected to the stem without footstalks.
    sex pilus :
    shear strain : An angular measure of deformation.
    short-period comets : Comets moving in orbits having periods less than 200 years.
    SI multiples :



    10–2ccenti102 hhecto

    sial : The Earth's continental crust, which is composed of granite rocks rich in silicon and aluminium. It is less dense than the underlying layer of sima and much thicker.
    sickle cell anaemia : A hereditary disease caused by a mutant form of haemoglobin. Under low oxygen tension in the blood, red blood cells containing sickle cell haemoglobin collapse, assuming a half moon, or sickle shape. The disease is mild in the heterozygous form but greatly shortens lifespan in the homozygous dominant form.
    sidereal period : The time taken by a planet or satellite to return to the same point in it's orbit, i.e. to complete one revolution with reference to the background stars. It can be determined from the body's synodic period.
    siemens (S): Unit of electrical conductance equivalent to the reciprocal of the ohm.
    sigma ( S, s ):
    Silurian period : A geological period lasting from about 4.45 to 4.15 x 108 years ago. Conditions were mainly marine and all the first true fish appeared. The first evidence of land plants also comes from the Silurian rocks. The Caledonian period of mountain building reached it's peak towards the end of the period.
    sima : The Earth's oceanic crust, which is composed of basilic rocks rich in silica and magnesium. It is denser than the sial of the continental crust and is believed to continue below it.
    simple sugar : A molecule composed of a single five or six-carbon sugar. sine rule, any angle divided by the sine of the angle is equivalent to any other.
    singularity (cosmology) : The point of infinite density at the central point of a black hole.
    sink : a natural removal process for pollutants in the troposphere such as dissolution and removal via rain.
    sintering : The heating, without melting, of a powdered substance, usually metal or plastic, so that it becomes a solid mass.
    sleet : frozen precipitation that falls as little chucks of ice.
    single lens reflex (SLR): a camera in which the photographer views exactly what will appear on the film.
    Lenses are interchangeable and close up attachments are easy to fit. They are very versatile and convenient for forensic photography. The most common type of these cameras is the 35mm. Similar in construction is the 2 ¼ inch which offers a larger film format. This will give a sharper picture than the 35mm and is therefore good for forensic photography.
    small-arms : Short range, low weight firearms, originally defined as capable of being handled by one individual, they include pistols, submachine guns, rifles, grenades and shotguns. An artificial calibre ceiling of 0.6 inches, in some classification systems 20mm has had to be abandoned with the introduction of small rockets and anti-tank guided missiles.
    smallpox : a severe infectious viral disease, controllable by cowpox vaccine.
    smog : a term used to describe a mixture of smoke and fog. Smog occurs when high concentrations of moisture is combined with smoke (often containing oxides of sulfur and nitrogen) in the presence of high temperatures or thermal inversions and the absence of wind. These conditions cause polluted air to stagnate over industrial areas and can create a respiratory health hazard. Large coastal industrial centers with surrounding high ground are more prone to smog. There is often a diurnal (over a day) variation in the process of smog formation because one of the necessary components for its formation is sunlight.
    smoke : the product of incomplete combustion and consisting mostly of carbon and small liquid and solid particles. Smoke is primarily caused by the burning of wood, coal, gasoline, or other biomass. Smoke particles are usually less than 1.0 micrometers in size. Wind intensity, particle size, air temperature, and atmospheric pressure all effect how smoke behaves in the environment.
    Snell's law : When a ray of light passes from one medium to another the angle q between the refracted ray and a line normal to the interface between the media is related to the angle (i) of the incident ray, also taken to the normal, by the equation sin i/sin r = n, where n is the relative refractive index of the media.
    SOCO ( Scene Of Crime Officer ) :Police Officer involved in case.
    sodium dodecyl sulphate (SDS) : A detergent that disrupts most protein-protein and protein-lipid interactions.
    solar longitude :This is an angular measurement that specifies the location of Earth in its orbit around the sun. More precisely, it is the longitude of the sun as given in geocentric coordinates. The evaluation of meteor data strongly relies on this figure rather than a conventional date.
    solar radiation : This is electromagnetic radiation (light energy) emitted by the sun. This energy is transmitted through space in the units of electromagnetic energy called photons. The strength of the solar energy that reaches our outer atmosphere is called the solar constant and has a value of approximately 2.0 calories per minute per square centimeter. Roughly one-half (1.0 cal min-1 cm-2) of all the solar radiation that enters the upper atmosphere is available at the earth's surface. Of the fifty percent loss, approximately 32 percent is reflected back into space by either clouds, dust, or aerosols; the remaining 18 percent is absorbed by clouds, dust, water, and atmospheric gases. The short high-energy wavelengths that are absorbed by the Earth are re-radiated at longer, lower energy wavelengths mostly in the IR wavelength region. These lower-energy wavelengths are, in part, prevented from escaping into space by the greenhouse gases in the atmosphere. Solar radiation is the fuel source that provides a mechanism for all biological processes on earth. Without solar radiation, life on earth would not exist. (This statement, of course, neglects the contribution to the earth's surface temperature from radioactive decay in the earth.)
    Solar system : A system comprising the sun and the astronomical bodies gravitationally bound to the sun, that is the nine major planets, heir satellites, ad the immense numbers of minor planets, comets and meteoroids. Almost all of the mass of the solar system (99.86%) resides in the Sun. The planets orbit the sun in the same direction and, with the exception of Pluto, move in paths close to the Earth's orbit (i.e. close to the ecliptic) and the suns equator. This and other information is taken as evidence of the common origin of the sun and the planets, some 4600 million years ago, following the contraction and subsequent flattening of a rotating cloud of interstellar gas and dust.
    Body distance from sun (x106 m) sidereal period spin period radius (km) no. of satellites mass (kg) mean density
    Sun --- --- 25.38d 696000 9 1.99 x1030
    Mercury 58 88 d 59d 2434 --- 3.3 x 1023 5490
    Venus 108 225 d 244d 6052 --- 4.9 x 1024 5246
    Earth 150 365 d 1d 6378 1 6 x 1024 5517
    Moon --- --- --- 1738 7.4 x 1022 3342
    Mars 228 687 d 24h 3395 2 6.4 x 1023 3937
    Jupiter 778 11.86 y 10h 70866 12 1.9 x 1027 1363
    Saturn 1430 29.5 y 10h 60016 9 5.7 x 1026 696
    Uranus 2870 84 y 10h 25402 5 8.9 x 1025 1335
    Neptune 4500 165 y 15h 22300 2 1 x 1026 1570
    Pluto 5900 248 y 6.4d 3200 (2750) --- 6.6 x 1023 4800 (7900)
    Solar Wind : The outflow of charged particles from the solar corona into space. Because of the high temperature of the particles of the corona (mostly protons and electrons), they are moving at speeds higher than the solar escape velocity. At the orbit of the Earth, these particles are moving at about 500 km/sec. Some of these particles are captured by the magnetic fields of the planets, forming their magnetospheres.
    soluble RNA : see transfer RNA
    solute : The substance that is dissolved by a solvent.
    solvent : That part of the solution that is present in the largest amount, most often the part that, if pure, is normally liquid.
    somatoplasm : A term used to describe all the cells of an organism except for the reproductive cells(germ plasm). In each generation the somatoplasm is derived from the germ plasm of the previous generation, but is distinct from it in that changes in somatoplasm (body cells) will not be passed on to the next generation.
    somites : Paired, block like masses of mesoderm arranged in a longitudinal series along the side of the neural tube of the embryo. Each somite will form one vertebra and its associated muscles.
    sorption : A class of processes by which one material is taken up by another. Absorption is refers to the process of the penetration of one material into another; adsorption to the action of one material being collected on another's surface.
    sound : A disturbance propogated through a medium by longitudinal waves. Strictly the term applies only to those waves that are audible to the human ear, i.e. with frequencies between about 20 and 20,000Hertz, those with frequencies above 20,000 Hz being called ultrasound and those below 20 Hz being called infrasound. Sound is propogated by vibrations of molecules in the medium, producing fronts of compression and rarefaction. Sound waves are longitudinal as the molecules vibrate in the direction of propagation. The three basic principles of sound are it's pitch (the frequency of the wave).
    sounding : a temperature profile of the atmosphere measured by a radiosonde. Also can indicate wind and dew point.
    sound intensity : The rate at which sound energy is propagated through a unit area perpendicular to the direction of propagation. It is measured in watts per square metre. The intensities of two sound levels are compared by a unit called a decibel. The intensity of a sound is not the same as its loudness, the latter being the magnitude of the sensation produced by the human ear, which is dependent upon the frequency of the sound.
    sound, speed of : 760 mph or 332 m-s
    space time continuum : A co-ordinate system that has four dimensions, three representing physical space and the fourth time. The four dimensional space-time continuum is used in relativity to define an event. For example an event occurring on the sun would be observed at different times on Earth and on Jupiter, as the light from the Sun takes some 35 minutes longer to reach Jupiter than to reach the earth. Thus the concept of simultaneity requires a four dimensional co-ordinate system to define events without ambiguity.
    spathe : The large bract that envelops certain flowers before opening.
    special creation : An account of the origin of life and its diverse forms by some act of divine creation.
    specialisation (of cells) : The change in cell capability from the performance of a wide variety of functions to concentrate on one activity or set of activities.
    speciation : The process by which the accumulated effects of variation within a population make cross breeding between two given organisms difficult or impossible.
    species : The smallest unit of taxonomic classification, referring to the most part a group of individuals capable of breeding amongst themselves. Species are defined by morphological, ecological, physiological, and biochemical criteria.
    specific gravity (relative density): The density of a substance divided by the density of water at 4oC. This value is numerically one thousandth of the density.
    specific heat capacity (c) : The quantity of heat needed to raise a unit mass of substance by 1oC. It is measured in joules per Kelvin per kilogram. For gasses the specific heat capacity at constant pressure (cp) exceeds that at a constant volume (cv) as heat is required to do work against the surroundings during the expansion. The rate of cp/cv (symbol: y) is 1.66 for monoatomic gases, 1.4 for diatomic gases and about 1 for other gases.
    speculum : A patch of brightly coloured feathers on a ducks wing. spectroscopy, The analysis of light by which the chemical make up of the light source can be identified by the dark lines created by individual elements within the light spectrum.
    spectrum : In general the way in which a particular property of a system is distributed over it's components. The visible spectrum, for example, is observed in a rainbow, which shows the distribution of frequencies when sunlight is split up into it's components by raindrops. The visible part of the spectrum however is only a small part of the electromagnetic spectrum, which ranges from X-rays to radio waves.
    spherical aberration : the tendency of a lens to focus the rays of light passing through the centre at one point while focussing rays from the outer portion at a different point.
    Many photographic lenses have six or more elements that have been introduced to cancel both colour and spherical aberrations. This is especially true for special lenses such as fast ( wide aperture ) lenses.
    spontaneous combustion : Combustion that results when materials undergo atmospheric oxidation at such a rate that the heat generation exceeds heat dissipation and the heat gradually builds up to a sufficient degree to cause the mass of material to inflame.
    spontaneous generation : A concept according to which living organisms develop from non-living matter.
    sporodochium (pl., sporodochia) : cushion-shaped mass of hyphae covered with conidiophores.
    spring equinox : In the Northern hemisphere, March 21 or 22; on these dates, the rays of the sun are striking vertically at noon at the equator (0 degrees latitude), for the earth is in such a position in its orbit that the axis is tilted neither toward nor away from the sun. For latitudes above the equator, the dates are earlier then these dates.
    squamous (pavement) epithelium : Epithelium composed of flat nucleated scales of various shapes, usually polygonal and varying in size. These cells fit together by their edges, like the tiles of a mosaic pavement.
    SS/Fix ( Signed Speed Fix ) : Method of sealing certain types of item packaging that could otherwise be easily tampered with, such as CJA and SSPB packaging. Uses a sticky label with the sealer’s initials and date, covered by sellotape.
    stability : possessing the ability to return to its original position; suppresses convection.
    standard solution : Any solution of known concentration.
    star : a luminous celestial body that is composed of gas and that derives it's energy from thermonuclear reactions in it's hot dense core. The Sun is a typical star. Stellar mass usually ranges from about 0.05 to 60 times the suns mass. A star's mass determines it's luminosity, surface temperature, size, and other properties as well as it's evolutionary path and lifetime: the higher the mass, the brighter, hotter, and larger the star and the shorter it's life. During the course of their history stars evolve, a process called stellar evolution. Young stars evolve from the protostar stage when they begin to generate energy by the thermonuclear fusion of hydrogen to form helium. This continues for some 1010 years for stars of solar mass but for only a few million years for the most massive stars. When the hydrogen is exhausted, stars evolve into giant stars, those of near solar mass becoming red giants. Further thermonuclear reactions occur involving fusion of helium, and possibly the heavier elements in more massive stars. A low-mass star finally evolves into a white dwarf. More massive stars explode as super-novae, the surviving cores possibly forming neutron stars or black holes depending on mass. Stars are not distributed uniformly through the universe but are grouped into enormous assemblies, called galaxies, as a result of gravitational forces.
    starch : The principle reserve carbohydrate of plants.
    star cluster : A group of stars that are associated by gravitational effects and that shared a common origin. Open clusters are loosely bound asymmetrical groupings of up top a few hundred stars occupying the disc of our Galaxy. Globular clusters are compact spherical groupings containing many thousands of very old stars and occur in the galactic halo.
    static equilibrium : A state of balance in which there is no activity. statistical analysis, The use of mathematics to determine whether deviations from a pattern, as predicted by a hypothesis, are correct.
    steady state theory : The model that holds that new matter is created in the spaces between the moving galaxies, so as to keep the density of the universe constant.
    steam explosion : Overpressure associated with the rapid expansion in volume on instantaneous conversion of water to steam.
    steering : directing other motion. The jet stream steers surface storm systems.
    Stefans constant (s) : 5.67 x 10-8Jm-2 s-1 degK-4
    steradian (sr) : The SI unit of solid angle equal to a solid angle that encloses a surface on a sphere equal to the square of its radius.
    stere : metric unit of volume equal to one cubic metre.
    steroids : A class of compounds containing four fused hydrocarbon rings.
    stibium (St): The original name given to Antimony.
    stimulus : Any physical or chemical change in the environment which brings about a change in the activity on the part of an organism (or portion of an organism, such as isolated tissue).
    Stoke's law : The resisting force acting on a sphere, radius r, moving through a fluid under gravity with velocity v is 6prhv, where h is the viscosity of the fluid. This law is used in the determination of viscosity.
    strain (physics) : The deformation of a body when it is subjected to stress.
    strangeness : A property of matter expressed as a quantum number (s), postulated to account for the unusually long lifetime of some hadrons. In the quark model strange hadrons contain the strange quark or it's antiquark. Strangeness is conserved in strong interactions and electromagnetic interactions.
    stratified epithelium : Several layers of cells superimposed on top of one another and varying greatly in shape. The cells of the deepest layer normally columnar and forming a single layer. Above these are several layers of spheroidal cells, becoming more compressed up to the superficial flattened cell layer.
    stratocumulus clouds : Low altitude gray colored clouds composed of water droplets that have a patchy appearance. Each cloud patch consists of a rounded mass. This cloud has a somewhat uniform base and normally covers the entire sky. Between the patches blue sky can be seen.
    stratopause : The boundary between the stratosphere and the mesosphere. It occurs at a height in the atmosphere of approximately 50 kilometers; however this depends on latitude. The atmosphere is characterized by a decrease in pressure with respect to increased altitude. More importantly, regions within the atmosphere like the troposphere, stratosphere, and mesosphere are distinguishable because of distinct temperature gradients with relatively well-defined starting and ending points. The stratopause is the highest portion of the stratosphere, with a temperature of approximately 0oC; the stratopause can also be described as the warmest region between the mesosphere and the stratosphere.
    stratosphere : The thermal atmospheric region of the atmosphere between the troposphere and the mesosphere. The lower boundary of the stratospheric region is marked by the tropopause and begins at approximately 13 kilometers; however, this altitude of the troposphere depends on latitude. The upper limit of the stratosphere is marked by the stratopause at approximately 50 kilometers. The stratosphere is characterized by relatively stable temperatures (between -80 and -50 degrees Celsius) in the lower regions, and begins warming near 20 kilometers, reaching its maximum temperature of approximately 0oC at the stratopause. Stratospheric chemistry is of particular interest to scientists because ozone, the principal substance that shields the earth from incoming solar ultraviolet radiation, is found in the stratosphere. It should also be noted that wind currents in the stratosphere are primarily horizontal in nature.
    stratospheric clouds : These are clouds found in the stratospheric region of the atmosphere. Unlike the moisture laden troposphere, the stratosphere is almost moisture free. A lack of moisture means that cloud formation in the stratosphere is a relatively uncommon occurrence. Because of the very low temperatures, nacreous clouds, a type of stratospheric cloud, occur during winter conditions at the higher latitudes. A second type of stratospheric cloud, called a polar stratospheric cloud (PSC), occurs in the polar regions during winter and early spring. Polar stratospheric clouds are of particular interest to scientists studying the Antarctic Ozone Hole. Polar stratospheric clouds form under extremely cold conditions, whereby nitric acid, water vapor and other trace chemicals freeze to form ice crystals. PSCs provide a solid surface on which chlorine-containing reservoir compounds can gather, and on this surface the chemical reactions involved in the depletion of ozone are greatly increased.
    stratospheric ozone : This is also called the ozone layer, where ozone concentrations are as high as 10 parts per million, and is a vitally important region of the atmosphere. This layer of ozone is located approximately 20-50 kilometers above the earth's surface. Stratospheric ozone is important because it prevents most of the high-energy ultraviolet solar radiation from reaching the earth's surface. Photodissociation, a photochemical process, is responsible for the formation of the protective ozone layer in the stratosphere. In the upper atmosphere, diatomic oxygen absorbs high-energy ultraviolet radiation. The absorption of radiation causes the diatomic oxygen molecule to break forming two oxygen radicals. The oxygen radical can then recombine with other diatomic oxygen molecules to form triatomic oxygen, or ozone. In the middle regions of the stratosphere, ozone is found in concentrations as high as 10 parts per million. Ozone can also form in the lower portions of the troposphere, due to anthropogenic activity and by a completely different mechanism. Without the protective stratospheric ozone layer in the upper atmosphere, life (as we know it) on earth would not be possible.
    stratus cloud : In general, clouds are classified and named according to their appearance and altitude at which they occur, being either high, medium, or low. Stratus clouds are low clouds, and as the root word suggests they are layered in appearance. They occur in broad sheets across most or all of the sky. Generally their formation is due to condensation within layered air that is not subjected to strong vertical movement.
    strychnine : An alkaloid poison derived from plants of the genus Strychnos. It acts upon the C.N.S., causing convulsions and ultimately death. It is still used as a poison for pests such as moles.
    styrene : chemical formula C8H8, also commonly called vinyl benzene. Styrene is an aromatic hydrocarbon originating from petroleum and natural gas by-products. It is used to manufacture resilient, lightweight packaging materials and fiberglass. Styrene is extremely volatile in air and evaporates quickly; as a result, it does not remain in the atmosphere for long periods of time.
    sublimation : The evaporation of a substance without melting. For any substance the liquid phase only occurs within certain limits of temperature and pressure - if the pressure is low enough, heating a solid will result in sublimation. Substances that sublime at atmospheric pressure include carbon dioxide (dry ice) and iodine.
    sub-machine gun : A light short range small arm developed from the infantry light machine gun. They are more accurate than the pistol and smaller than the rifle. They almost all use 9mm ammunition, fire automatically, and depend on blow-back action (i.e. use the expanding gas of the ammunition to activate the reloading mechanism).
    subsidence : sinking air.
    substrate : The molecule upon which an enzyme acts during an enzyme catalysed reaction.
    succession : Ecological development that begins in a habitat or area not previously occupied by the given community of a previously unoccupied area.
    Secondary succession : refers to the replacement of one community by another.
    sucrose : A carbohydrate consisting chemically of one molecule each of glucose and fructose linked together. It is commercially the most important of the sugars, being used as a sweetener in food and drinks. When heated to 160oC it forms barley sugar and at 200oC becomes caramel.
    sulphur dioxide : This is a colorless gas consisting of a single sulfur atom and two oxygen atoms. Sulfur dioxide is a major primary pollutant in the atmosphere originating mostly from coal fired power plants and other fossil fuels combustion. In the atmosphere, sulfur dioxide is usually oxidized by ozone and hydrogen peroxide to form sulfur trioxide, a secondary pollutant. Sulfur trioxide, similar to sulfur dioxide, is extremely soluble in water. If these sulfur oxides are present in the atmosphere when condensation occurs, droplets of sulfuric acid (acid rain) are formed. Volcanic eruptions provide a natural source of sulfur dioxide in the atmosphere. However the real problem associated with the production of sulfuric acid in the atmosphere is not with the sulfur dioxide expelled by volcanoes. Anthropogenic production of sulfur dioxide, caused by the burning of fossil fuels, is largely responsible for damage caused by acid rain.
    sulphuric acid : In the atmosphere sulfur oxides (see sulfur dioxide) are converted to sulfuric acid. Oxides of sulfur and nitrogen combine with atmospheric moisture to produce acid rain. Although some sulfur oxides are introduced into the atmosphere by natural means, such as volcanic eruptions, the majority of the sulfur oxides responsible for the damaging effects of acid rain come from anthropogenic sources, mainly the burning of fossil fuels. Areas in the northeastern United States, eastern Canada, and northern Europe have suffered damage due to the effects of acid rain. In many areas damage to forests, crops, lakes, and streams are so severe that they are completely devoid of any life forms. Steps are now being taken in many parts of the world to reduce the amount of sulfur dioxide introduced into the atmosphere. In 1990, amendments where made to the Clean Air Act that places restrictions on the release of sulfur dioxides by power plants. The amendment calls for the reduction of sulfur emissions from a 1990 level of nearly 20 million tons per year to approximately 10 million tons per year by January 1, 2000.
    summer solstice : In the Northern Hemisphere occurs on about June 21 of each year. The summer solstice is the longest day of the year and marks the beginning of the summer season. If the earth's axis were not tilted in relation to the plane of earth's orbit around the sun (the ecliptic) there would be no seasonal changes on earth. But because the earth's axis is tilted in relationship to its plane of orbit around the sun (~23.5 degrees) and assumes a constant direction, with the North Pole pointing towards the North Star, seasons occur, and daylight hours can fluctuate in length. Each day prior to the summer solstice the sun appears farther north in the sky; but at the summer solstice, the sun reaches its most northerly position in the sky, directly above the Tropic of Cancer, 23.5 degrees north latitude. Following the summer solstice the sun moves farther south in the sky, and on about September 23 it is directly overhead at the equator (the fall equinox).
    Sun : the nearest star to the Earth and the centre of our Solar system. It dwarfs the other bodies, having a diameter of 864,000 miles and representing approximately 99.86 percent of all the mass in the solar system. As a star, the Sun generates energy by the process of fusion. The temperature at it's core is 15 x 106 K, and the pressure there is 340 billion atmospheres. The surface temperature is 5,500oC. At the solar core, hydrogen can fuse into helium, producing energy. The Sun consists of three layers: the photosphere, the chromosphere, and the corona, and spins on it's axis from left to right.
    sunspot cycle : This cycle, lasting an average period of 11 years, involves recurring increases and decreases in the number of sunspots that occur on the sun's surface.
    sunspots : A dark area, which is strongly magnetic, that occurs in the area of the photosphere on the disk of the sun.
    supercell : a large thunderstorm in which the updrafts and downdrafts are in such close balance that the storm may have a lifetime of several hours. supercooled water, water that is below the freezing temperature but is still in liquid form.
    supercooling : The reduction of a temperature of a liquid below its freezing point without it's solidification. The effect can be achieved by slow and continuous cooling with pure liquids, since any solid matter would cause the liquid to solidify around it. A super cooled liquid is in a meta-stable state and any disturbance will cause solidification.
    superfluid : A fluid that exhibits a very high thermal conductivity and virtually no friction at temperatures close to absolute zero. Such a fluid will flow up the sides and out of an open container. Liquid helium becomes a superfluid at 2.19 Kelvin's, called the lambda point.
    supergiant : The largest and most luminous type of star, bright enough to be visible in nearby galaxies. They evolve from very massive but more complex stars are very rare.
    supernova : A cataclysmic stellar explosion, seen as a sudden increase in the e stars brightness by a million times or more. It occurs in the late evolution of stars, one type almost certainly involving a massive supergiant stars, another type, possibly disrupting white dwarfs. Most or all of the stars substance is blown off at high velocity, forming an expanding gas shell - the supernova remnant. If the stars core survives it will most probably end up as a neutron star or a black hole.
    Svedberg unit : Unit used to describe in multiples of 10-13 sec. the velocity attained per unit of applied force by a particle moving though a liquid medium.
    syllogism : A logical scheme or analysis of a formed argument, consisting of three propositions called respectively the major premise, minor premise and the conclusion. e.g. Every virtue is commendable, patience is a virtue, therefore patience is commendable.
    symbiosis : A relationship between two species of organisms in which both derive benefits from the other.
    syndactyly : Commonly called "webbed Fingers", where the digits are joined together with skin. A rarer form of this can occur when the fingers are fused together by the bone.
    synodic period : The average time taken by a planet or satellite to return to the same point in its orbit, relative to the sun, as seen from earth or from the satellites primary (i.e. the body it orbits).
    synoptic scale : a large scale event that is usually measured in hundreds to thousands of kilometres and days to weeks; e.g. fronts, cyclones, and anticyclones.
    synthesis : The process by which larger molecules can be built up from smaller molecules or atoms.
    system : An association of independent organs throughout the body for the performance of a necessary body function. Some systems in higher animals are the circulatory, digestive, muscular, skeletal, and excretory systems.
    systematic errors : an error which affects all measurements equally, making all measurements either higher or lower than the true value.
    systematics : A term originally used to refer to the study of different systems of classifying animals and plants. Today the term "systematics" is used more or less synonymously with the term taxonomy.


    tail : the most distinctive feature of comets, especially great ones. It is typically directed away from the sun. Ancient and medieval observers frequently described a comet as a broom or sword, depending on the look of the tail. Typically, telescopic comets will exhibit either no tail or one extending a few arc minutes. Naked-eye comets can show a tail extending up to several tens of degrees. Comets can display two basic types of tails: one gaseous and the other largely composed of dust. The dust tail can be curved, spread out, and yellowish in appearance, while the gas tail is usually very straight and bluish.
    tamper evident bag : type of packaging used by certain police forces for submitting items to the FSS. Method of sealing is such that the SS/Fix is not required.
    tap root : A stout, elongated, primary root.
    tau ( T, t ) :
    tau particle : An elementary particle with a very short lifetime (5x10-12 sec.) and a mass about 3500 times that of the electron. It is classified as a lepton. It reacts by weak interaction.
    tautology : A statement that is always true and therefore gives no information. For example "IT is either raining or it isn't."
    taxonomy : The science of classification; in biology this refers to the classification of organisms into kingdom, phylus, class, order, family, genus and species.
    tectonic activity : The process of the formation, movement, interaction, and destruction of parts of the earth's crust on a generally large scale. This can be used to explain seismicity, volcanism, and mountain building.
    tectonics : The structural arrangement of rocks in any crust of a planet. Used to understand rock structures.
    teleology : Assigning purpose to an action, such as saying the cell takes in Calcium ions "in order to...."
    temperature inversion : The abnormal reversal of temperature in the troposphere caused by the entrapment of urban air pollution. Under normal circumstances, air in the troposphere is cold at high altitudes and warm at low altitudes, or near the earthís surface. When air pollutants, such as SO2 or NOx, in urban areas get too concentrated, smog is produced. Since cold air underlies the warmer air at high altitudes, the air does not mix well which can lead to human health disturbances in people with respiratory illnesses such as asthma.
    tendon : The sinew joining muscle to a bone.
    telophase : The final phase of mitosis, in which the cytoplasm of the dividing cell is cleaved and two daughter cells are formed.
    tera (T) : 1012
    teratogen : a chemical or physical agent that can cause defects in a developing embryo or foetus when the pregnant female is exposed to the harmful agent.
    terminal burst : The flare at the end of a meteor's path.
    territoriality : The tendency of some organisms to defend a section of space surrounding them and/or their family.
    termolecular reaction : A reaction containing three particles. In the atmosphere an example of a termolecular reaction is one in which a molecule acquires the excess energy released by a reaction so that the products created do not convert back to the original state of the reactants. The reaction of molecular oxygen with an oxygen atom (radical) to produce ozone is a good example of an important atmospheric termolecular reaction. In the atmosphere this third body is most often molecular nitrogen because statistically this is the most likely next collision since atmospheric N2 = 78% by volume.
    terpene : A naturally occurring organic compound, of the general empirical formula, C10H16, biologically built from a naturally occurring "monomer" called isoprene, C5H8, which is found as a volatile oil in plants. A clearly important, and olifactorily obvious, example is alpha-terpinene found in lemon oil.
    tertbutyl alcohol : a highly flammable, volatile, colorless liquid which has a camphor-like odor. It is miscible in esters, and aromatic and aliphatic hydrocarbons, and soluble in water. Based on its vapor pressure, tert-butyl alcohol will exist mainly in the vapor phase in the atmosphere. It is most likely to react with the hydroxyl (OH) radical at this state. The reaction products are formaldehyde and acetone.
    Tertiary Period : This extended from about 65 million years ago to about 2.5 million years ago.
    Tertiary period : The first geological period of the Cainozoic era lasting from about 65 to 1.8 x 106 years ago and contains the Pleistocene, Eocene, Ogliocene, Miocene, and Pliocene epochs, in ascending order. Most of the rocks of the period were laid down in shallow water. Modern invertebrates and mammals evolved and became increasingly abundant; the modern angiosperms became the dominant plants. The Alpine period of mountain formation extended through the period and reached it's peak in the Miocene. The climate began to deteriorate in the Oligocene, finally leading to the ice age of the Pleistocene.
    tesla : The SI unit of magnetic flux density equal to one weber per square metre and equivalent to 10,000 gauss.
    testosterone : An androgen; a hormone produced in the interstitial cells of the testes of males and responsible for the characteristic changes associated with puberty.
    tetrad : In meiosis, the four part structure resulting from the duplication of each pair of homologous chromosomes.
    thermacidophiles : Bacteria which grow optimally at 105oC and at pH2.
    thermodynamics : That branch of physical science which deals with heat as a form of energy. It is concerned with such problems as the exchange of energy (measured always in respect to the gain or loss of heat from a system) during chemical or physical processes.
    thermodynamics : The science of heat and temperature and of the laws governing the conversion of heat into mechanical, electrical, or chemical energy.
    thermosphere : The outermost shell of the atmosphere, between the mesosphere and outer space; where temperatures increase steadily with altitude.
    theta ( Q, q ) :
    thickness : the vertical distance between two levels of constant pressure. The greater the average temperature of the layer, the "thicker" it is.
    threshold limit value – ceiling ( TLV-C) : limit for the atmospheric concentration of a chemical which may not be exceeded at any time, even instantaneously in workroom air.
    threshold limit value – short term exposure limit ( TLV – STEL ) : A maximum limit on the concentration of a chemical in workroom air which may be reached, but not exceeded, on up to four occasions during a day for a maximum of 15 minutes each time with each maximum exposure separated by at least one hour.
    threshold limit value – time weighted average ( TLV – TWA ) : A limit for the atmospheric concentration of a chemical, averaged over an 8hr day, to which it is believed that most people can be exposed without harm.
    thylakoid disc : Flattened pancake like sacks with double layered walls, formed from the inner membrane system of the chloroplast. The lamellae and grana inside chloroplasts are composed of thykaloid discs.
    thymine :
    time dilation : An effect produced by Einstein's special theory of relativity. If two observers, A and B, are moving at a velocity v, relative to each other, it will appear to a that Bs clock will show that time is running more slowly; thus a time t, measured on A's clock, will be t(1 - v2/c2)0.5 on B's clock, where c is the velocity of light.. The effect has been observed in some particles moving at high velocities which appear to have an anomalously long lifespan.
    tissue : An aggregate of similar cells bound together in an ordered structure and working together to perform a common function.
    TNT (trinitrotoluene, C6H2(NO2)3CH3 ) : A highly explosive pale yellow crystalline solid. It is prepared from toluene treated with concentrated sulphuric and nitric acids and is used in shells, bombs, etc., and blasting explosives.
    toluene : a highly volatile and water-soluble benzene derivative that is highly toxic to most forms of life. Its estimated lifespan in air is 60 hours in the case of a photochemical reaction with hydroxyl radical and is eventually oxidized to carbon dioxide. Toluene is used in a variety of industries including the manufacture of TNT, pharmaceuticals, rubbers, and other benzene derivatives, and is also a fuel additive and a paint solvent. Toluene also reaches the atmosphere from natural sources such as coal tar, mineral oils, and forest fires.
    torr : The pressure of air that supports 1mm of mercury in a barometer at sea level. 1 atm = 760 torr = 101.325 kPa.
    total column ozone : The total amount of ozone that is found in a column of air above the earth from the surface to the top of the atmosphere. The majority of this amount is typically found in the stratosphere.
    total inhalable dust : The fraction of airborne dust which enters the nose and mouth during breathing and is available for deposition in the respiratory tract.
    toxic air pollutants : in the atmosphere, toxic air pollutants are present in small amounts that can have adverse effects on the health of human populations and the environment. Toxic air pollutants include polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, polychlorinated biphenyls (PCBs), and heavy metals, such as, mercury, copper, lead, zinc, arsenic, and cadmium. These pollutants are carried by particulate matter and can be mixed with precipitation. The Integrated Atmosphere Deposition Network (IADN) studies the transportation of specific toxic substances located in the atmosphere.
    trace gases : These are gases in the atmosphere that do not occur in large quantities but are significant to life on Earth or are important constituents of the chemical cycles in the atmosphere.
    trade winds : Wind systems occupying most of the tropics, which blow from 30 degrees North and South toward the equator; winds are northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.
    trajectory : The flight path of a missile dependent upon the speed of the missile, the air resistance acting upon it, the forces exerted by gravity and any wind pressure pushing it laterally.
    transamination : The stepwise series of reactions in which the amino groups from one amino acid type is transferred to an intermediate substance, thus producing another type of amino acid.
    transduction : the transfer of genes between bacteria by bacteriophages.
    transfer RNA (soluble RNA) : A type of RNA in the cytoplasm of which there are at least 20 varieties, one specific for each amino acid. tRNA unites with its specific amino acid and draws it to the ribosome during protein synthesis.
    transformation : a mode of gene transfer in bacteria in which a piece of free DNA is taken up by a bacterial cell and integrated into the recipient genome.
    transitional epithelium : Epithelium in which the cells , in three or four layers, are so fitted together that the appearance is not one of distinct stratification. Found in the ureters and urinary bladder of humans.
    translation : An aspect of protein synthesis in which the genetic information coded on messenger RNA is used top specify the order of amino acids in a polypeptide. Translation occurs in the ribosomes, where messenger RNA, ribosomal RNA, and activated amino acids meet and peptide bonds are formed.
    transmitted lighting :
    transmutation : The conversion of one element into another. They were achieved eventually by bombarding elements with alpha particles or neutrons. An example is the production of oxygen 17 when nitrogen 14 is bombarded with alpha-particles.
    transmutation (of species) : An older term for the idea that over a long period of time new species arise though modification of old species.
    transuranic elements : Elements with a higher atomic number than uranium. Apart from traces of neptunium and plutonium, none of them has ever been detected in nature since no isotopes of sufficient half life exist: they have been created since 1940, usually in minute amounts, in nuclear reactions.
    trefoil (botany) : A simple form of division.
    Triassic period : A period of geological time at the beginning of the Mesozoic era, lasting from about 2.4 to 2 x 108 years ago. The rocks of the period, laid down mainly under continental conditions often considered with those of the preceding Permian period as the Permo-Triassic. The dinosaurs, ichthyosaurs and plesiosaurs appeared in the Triassic.
    tribology : The study of friction and such applied topics as lubrication, abrasives, surface wear, etc.
    trichloroethylene (C2HCl3) : this is an industrial solvent used primarily for vapor degreasing and cold cleaning. It is an extraction solvent for greases, oils, fats, waxes, and tars, and is used by the textile processing industry to sour cotton, wool, and other fabrics. Exposure to moderate amounts of trichloroethylene may cause various health effects such as headaches, vertigo, visual disturbance, tremors, and dizziness. Death may occur from inhalation of large amounts. People located near or downwind of sites where TCE may be in operation might be exposed to higher levels. It is a carcinogen.
    trichlorofluoromethane (Freon -11) : One of the principal greenhouse gases, a gas with absorption bands in the infrared portion of the spectrum. There is extensive evidence showing that a class of synthetic compounds, the chlorofluorocarbons (CFCs), are responsible for the destruction of the ozone layer. CFCs are molecules that contain one or more atoms of both chlorine and fluorine. In September of l992, the ozone hole over Antarctica was the largest ever recorded and was almost THREE times as large as the area of the U.S. Because CFCs are so unreactive, they do not break down when released into the air in the troposphere where they are spilled. In time, air currents and diffusion carry them into the stratosphere, where, under the influence of UV radiation, they release chlorine radicals that initiate the destruction of ozone. Data collected by NASA have shown conclusively, that there is an inverse relationship between ozone concentration and the chlorine monoxide radical in the stratosphere; ClO is formed by chlorine atom attack on O3. CFCs are very useful inert, nontoxic, nonflammable compounds that had been used for years as coolants and as spray can propellants for aerosol forms of hair sprays and deodorants. They had been unsurpassed as solvents for cleaning electronic microcircuits. Commercially, the most important CFCs are the halogenated methanes, Freon-11 (trichlorofluoromethane) and Freon-12 (dichlorodifluoromethane). Over 50% of asthma inhalers contain chlorofluorocarbns as the solvent and gaseous propellent. These CFCs have relatively recently been prohibited in all products except in those medicinal inhaler dispensers for asthmatics and a few other limited exceptions. In Finland alone there are over a million medicinal dispensers that disperse freons into the atmosphere. This is equal to the freon concentration of the cooling devices in approximately l00,000 refrigerators.
    Trojan group : Minor planets that lie close to either of two points in Jupiter's orbit. Each point forms an equilateral triangle with Jupiter and the Sun.
    trophic level : Levels of nourishment in a food chain. A food chain is the transfer of energy from its ultimate source in plants through a series of organisms, each of which eats the preceding organism.
    trophoblast : In mammals the thin walled side of a blastocyst which gives rise to the placenta and the membranes that surround the embryo.
    tropopause : The area where the temperature in the troposphere no longer decreases, indicating the boundary between the troposphere and the stratosphere.
    troposphere : The lowest layer of the Earth's atmosphere, ranging from the ground to the base of the stratosphere with a altitude of 10-15 kilometers depending on the latitude. This is where all weather occurs. The word troposphere is derived from the Greek words tropos, turning and spharia, sphere.
    trough : an area of low pressure. Cyclonically curving winds.
    tuber : The fleshy underground part of the stem of a plant.
    tunnel effect :
    twin lens reflex camera :

    Tyndall effect : When a parallel beam of light, such as a wavelength that none is absorbed, is passed through a gas, liquid, or transparent solid, part of it is scattered in all directions so that it may be seen from the side.


    UARS (Upper Atmosphere Research Satellite) : A satellite deployed by NASA to study the chemistry in the upper atmosphere of Earth.
    UEL ; Upper Flammable (or Explosive) Limit : The maximum concentration of vapor/gas in air at a given pressure and temperature in which a flame can be propagated.
    ultra -centrifuge : A high speed centrifuge used to determine the size of small particles and large molecules by their rate of sedimentation.
    ultra-microscope : An optical microscope used to detect particle smaller than the wavelength of light by illuminating them at an angle, so that the light scattered by the particles can be observed against a dark background.
    ultraviolet : Just beyond he violet end of the physical spectrum.
    ultraviolet radiation : Electromagnetic radiation, the frequency of which lies between that of the violet end of he visible spectrum and X-rays, i.e. between about 380 and 5 nanometres. Ultraviolet radiation is produced during arc discharges and by gas discharge tubes (e.g. the mercury vapour lamp). It is also produced in large quantities by the sun, although the radiation below 200nm is absorbed by he ozone layer.
    umbel : A flat topped cluster of flowers, having their footstalks of pretty equal lengths and radiating like the ribs of an umbrella.
    umbra : A region of complete shadow where no light reaches the surface.
    unicellular : An organism consisting of just one cell.
    unified field theory : The theory that encompasses he four fundamental interactions - strong, weak, electromagnetic, and gravitational - in terms of a single field, analogous to the electromagnetic or gravitational fields.
    unit membrane : The model that sees cell membranes (plasma, nuclear, etc.) as consisting of a mosaic of small sandwiches; that is phospho-lipid molecules between an inner and outer layer of protein.
    univalent : Having a chemical valency of one.
    universal gravity law : The model that holds that every piece of matter in the universe pulls every other piece of matter in the universe towards it.
    updrafts : the warm moist air that is involve din the formation of cumulonimbus clouds.
    upsilon ( U, u ) :
    upwelling : a rising-up of colder water.
    uracil : A base found only in RNA. Abbreviated U for the free base, rU for uridine, and dU for deoxyidine.
    uranium-thorium dating : An absolute dating technique which uses the properties of the radioactive half-life of Uranium-238 and Thorium-230. The half-life of uranium-238 is 4.5 billion years, that is, in that many years half of the original amount is still uranium-238 while the other half has lost nucleons to form a different element which is more stable.
    Uranus : The seventh planet from the Sun, and the first to be discovered using a telescope (by William Herschel in 1781). Uranus has an equatorial diameter of 51, 200 km and orbits the Sun once every 84 years at a distance varying between 18.3 and 20.1 astronomical units. It rotates once every 17.24 hours, and has a mass 14.5 times that of the Earth, giving it a density 1.3 times that of water. Unlike every other planet in the Solar System, Uranus lies almost on it's side in it's orbit, pointing first one pole and then the other towards the Sun as it moves around it's orbit. This may be the result of the impact of a large comet with Uranus long ago. It has at least eleven moons.
    Uranus (Astronomy): The third largest planet in our solar system and the seventh from the Sun, which it orbits every 84.01 Earth years. One day on Uranus is 17 hours, 14 minutes, and 24 seconds long. The gravity of Uranus is .86 of the Earth's and the planet is 120% as dense as the Earth. It has a diameter of 32,116 miles and 15 moons. Uranus lies tipped on its side with its north and south poles alternately facing the Sun during an 84-year swing around the solar system.
    urban air pollution : pollution that occurs in cities from the burning of fossil fuels and the emissions of hydrocarbons. Urban air pollution can be in the form of ozone, smog, acid rain, carbon monoxide, particulate matter (PM-10), and nitrogen oxides.
    uric acid (C5H4N4O3) : A degradation product of purine in mammals, in which the ring structure is preserved. The compound is formed during the nitrogen metabolism of animals and the chief nitrogenous excretory product of reptiles and birds. In man, raised levels of uric acid in the blood are associated with gout.
    uterus : The womb; the hollow muscular organ of the female reproductive tract in which the foetus undergoes development.
    UV-A : Ultraviolet light that has wavelengths of 320nm to 400nm. The wavelengths of this light are shorter than visible light and are not absorbed in the stratosphere by ozone.
    UV-B : An ultraviolet wavelength of light between 280 nm and 320 nm whose intensity is increasing at the earth's surface (probably causing increases in skin cancer), This UV increase is because of decreases in statospheric ozone.
    UV-C : Light that spans the spectrum with wavelengths of 10nm to 290nm. These wavelengths of ultraviolet light are extremely dangerous to human and animal tissue and is totally absorbed in the stratosphere by ozone and molecular oxygen.
    UVCE ; Unconfined Vapor Cloud Explosion : Explosion involving a large mixed vapor/air cloud in the open.
    UV/Vis spectrophotometry : Ultraviolet/visible spectrophotometry is used to measure the absorption capabilities of certain compounds with reference to wavelengths of light on the ultraviolet and visible light ranges.
    UV radiation : energy that is emitted in the form of electromagnetic waves with a wavelength of 1-380nm, which is composed of UV-A, UV-B, and UV-C light; UV-A light being the longest wavelength and having the smallest energy and UV-C light being the shortest wavelength and having the highest energy. All UV-C light and most UV-B light is filtered out of the atmosphere via the ozone layer. However, UV-A light travels to the surface of the earth.


    vacuolar membrane : A unit membrane structure that separates the contents of vacuole from the surrounding cytoplasm.
    vacuole : A bubble like structure surrounded by a membrane, occurring in the cytoplasm, and serving as a reservoir to hold food and waste products. vacuum, A region of space that contains no matter. In practice a perfect vacuum is impossible to obtain and any region where the pressure of the gas is less than about one millimetre of mercury may be considered a vacuum. In technical work a soft (or low) vacuum goes down to a pressure of 10-4 mm Hg, a hard (or high) vacuum is between 10-4 and 10-9 mm Hg, and an ultrahigh vacuum is below 10-9 mm Hg.
    Vadose zone : The unsaturated zone in a soil where chemical processes are at their most active. Its extent is determined partly by the content of the soil water, but it cannot extend beyond the water table, below which voids are completely filled with water.
    valence electrons : The outermost electrons of an atom that are in the orbitals of highest principal quantum number of all electrons in the atom and don't fill that orbital completely.
    valency : the combining power of an atom.
    vanadium (V):
    Van der Waal's equation : A modification of the ideal gas equation in which V is adjusted to (V-b) to take account of the volume occupied by the gas molecules. Assuming that forces of attraction exist between the gas molecules the pressure term is then adjusted to (p - a/V2). Both a and b are constant for a particular gas.
    Van Urk test : Specific for LSD which will turn the reagent blue-purple.
    vas deferens : A long tube like structure at the top and back of the testes, in which sperm are stored and through which they pass out through the penis.
    veering : clockwise shifting of the winds with time or distance.
    vegetal pole : The surface of an egg opposite the animal pole, on the axis running through the nucleus. The yolk density within the egg is greatest at the vegetal pole.
    veins : Vessels which carry blood from the various organs to the heart.
    velocity (v) : The speed of a body in a specified direction, i.e. it's rate of displacement (s) in a specified direction is given by v = ds/dt. Velocity is a vector quantity, whereas speed is a scalar quantity. In SI units velocity is measured in metres per second.
    Venus : Distance from Sun 108 x 106 km, diameter 12102 km
    Venus : Second planet out from the Sun. In size Venus is almost a twin of the Earth, with 82% of the Earth's mass. It orbits the Sun once every 225 days at an average distance of just over 0.72 astronomical units, in a nearly circular orbit. It rotates backwards (retrograde) once every 243 days, relative to the fixed stars, so in a sense a 'day' on Venus is longer than a 'year'. Because of the motion of Venus in its orbit, however, if you could see the Sun from the surface of the planet, the time from noon to noon would be 116.8 of our days, so there would be just under two Venusian days in each Venusian year The equatorial diameter of Venus is 12, 104 km. Unlike the Earth, Venus has a very thick atmosphere rich in carbon dioxide. This produces a strong greenhouse effect, which, combined with the fact that it is closer too the Sun than we are, raises the surface temperature to 730 Kelvin. The pressure of this atmosphere at the surface of Venus is 90 times the atmospheric pressure at sea level on Earth. Venus is completely cloud covered and has a high albedo, reflecting 79% of the incoming sunlight. As a result, after the Sun and the Moon, Venus is the brightest object in the sky, seen close to the Sun as the evening star or morning star, depending on it's position in its orbit. It has no moons. albedo, a measure of the reflectivity of an object. A perfectly reflecting surface has an albedo of 1, while a black surface that absorbs all light that falls on it has an albedo of 0.
    Venus (Astronomy) : The second planet from the Sun. Whist Venus resembles the Earth in size, physical composition and density more closely than any other known planets it's rotation is retrograde and it is also closer to a perfect sphere. It has a nickel-iron core but no magnetic field. The surface temperature is 900° F with an atmospheric pressure 97 times that of the Earth's and the 0.91 of the Earth's gravity. It's orbit, which is nearly circular is 224.7 Earth days. It has a mass of 4.872 x 1027g; radius of cloud surface about 6100 Km; radius of solid surface about 6056 Km; surface temperature 737K; temperature of cloud tops 250K; cloud composition more than 75% H2SO4 and about 25% water; atmosphere (by volume) 90-95% CO2 with traces of SO2, water, CO, H2SO4, Ar, Ne, HF, HCl. Atmospheric pressure 92-95 atm.
    vernal equinox : A time during the spring season when the sun is directly above the equator which results in an equal amount of time for day and night.
    vertical flux : In dry deposition this refers to the rate at which a gas particle is deposited onto another surface without the aid of precipitation. Vertical flux equals concentration of the species multiplied by the deposition velocity.
    vertical mixing : The movement of air in a vertical direction usually caused by differences in temperature and density.
    vestigial organ : A structure in a degenerate state that remains in an organism but has little or no present function. The appendix in human beings is a vestigial organ.
    video surveillance units : These are becoming increasingly cheaper and of a higher quality are widely used in locations such as shops, traffic lights, police stations. They are even available for baby alarms.
    vinyl bromide : a toxic compound that was established as a federal hazardous air pollutant in 1993. Sources of vinyl bromide may include rubber substitution, flame-retarding treatment of acrylics, laminating, and/or preparing films. It is also important to point out that vinyl bromide may be the result of the atmospheric degradation of 1,2-dibromoethane. Based on a typical atmospheric gas phase reaction with a hydroxyl radical, the lifetime of vinyl bromide in the atmosphere is between 1.5 and 2.1 days resulting in the products formaldehyde and formyl bromide.
    visibility : A measurement of the ability to see and identify objects at different distances.
    virus : A non-cellular, sub-microscopic particle composed of a protein coat surrounding a nucleic acid core. Viruses can reproduce only inside living cells (eukaryotes or prokaryotes).
    vitalism : The view that life is an expression of something above and beyond the chemical and physical interactions of a group of molecules.
    vitamin : A chemical substance, required in only trace amounts, that are thought to aid enzymes in catalysing specific chemical reactions.
    vitamin A : A fat soluble vitamin and an essential constituent of the visual pigments of the eyes. It also functions in the maintenance of healthy mucous membranes. Vitamin A deficiency leads to dryness of membranes lining the mouth and respiratory tract, blindness and effective growth.
    vitamin B complex : A group of water soluble vitamins that are all constituents of coenzymes involved in metabolic reactions. Thiamine (B1) is important in carbohydrate metabolism. Deficiency leads to Beriberi. Riboflavin (B2) is involved in carbohydrate and amino acid metabolism. Nicotinamide (nicotinic acid or niacin) can be synthesised from the amino acid tryptophan. Vitamin. B6 (pyridoxine) is essential for amino acid metabolism. Also common in many foods are pantothetic acid, a constituent of coenzyme A; biotin, which is synthesised by intestinal bacteria; and choline, a precursor of acetylcholine (which transmits nervous impulses). Folic acid and Vitamin. B12 (cyanocobalamin) can be synthesised by intestinal bacteria; deficiency of either causes megaloblastic or pernicious anaemia.
    vitamin C (ascorbic acid) : A water soluble compound that is required for several metabolic processes, especially for the maintenance of healthy connective tissue. It cannot be synthesised by man and certain animals, in whom it must for part of the diet. Deficiency leads to Scurvy.
    vitamin D : A fat soluble vitamin consisting of several related compounds (sterols), principally cholecalciferol (D3) and ergocalciferol (D2). Vitamin. D is important in calcium and phosphorus metabolism, especially in the absorption of calcium from the gut and the deposition and resorbtion of bone minerals. efficiency in infants causes rickets.
    vitamin E : A vitamin consisting of a group of related compounds that function as biological antioxidants, inhibiting the oxidation of unsaturated fatty acids. The most potent form of vitamin E is alphatocopherol. Deficiency, which is rare, may lead to anaemia.
    vitamin K : A vitamin consisting of a group of quinone-based compounds that are necessary for the formation of prothrombin, important in blood clotting. It can be synthesised by intestinal bacteria.
    viviparous : Term applied to organisms whose embryos develop within the body of the mother and derive their nourishment from their mother. Volcanoes - Openings in the earth's crust that release molten rock, steam, reduced and oxidized compounds, and ash from within the earth's interior into the atmosphere.
    volt (v) : The unit of potential, potential difference, or electromotive force equal to the potential difference between two points on a conductor carrying a steady current of one ampere when the power dissipated is one watt. volumetric analysis, the process of reacting a solution with a solution of known concentration with one of unknown concentration, in order to determine the equivalence point.
    vorticity : spin of the air indicating rotation. Positive vorticity is cyclonic flow, while negative vorticity is anticyclonic.
    vulva : The external female sex organs (genitalia).


    Walker Cell : a zonal circulation of the atmosphere confined to equatorial regions and driven principally by the oceanic temperature gradient. In the Pacific, air flows westward from the colder, eastern area to the warm, western ocean, where it acquires warmth and moisture and subsequently rises. A return flow aloft and subsidence over the eastern ocean complete the cell.
    water : a triatomic molecule(H2O)that covers three quarters of the Earth's surface, 60-70% of the world's weight, regenerates and redistributes through evaporation and other atmospheric processes. Water is involved in electrical charge separation because it has two types and positions of atoms giving it a net dipole movement. Water vapor also absorbs 17% of solar radiation in the troposphere, thus making it one of the two principal greenhouse gases. Of the solar energy absorbed by the Earth's surface a little more than half goes into latent heat, which is heat absorbed by water because of its transformation from a liquid to a gas. When these molecules condense back into a liquid, usually higher in the atmosphere, they released that energy back into the atmosphere as local warming.
    water cycle : the process by which water is transpired and evaporated from the land and water, condensed in the clouds, and precipitated out onto the earth once again to replenish the water in the bodies of water on the earth.
    water vapour : water present in the atmosphere in gaseous form; the source of all forms of condensation and precipitation. Water vapor, clouds, and carbon dioxide are the main atmospheric components in the exchange of terrestrial radiation in the troposphere, serving as a regulator of planetary temperatures via the greenhouse effect. Approximately 50 percent of the atmosphere's moisture lies within about 1.84 km of the earth's surface, and only a minute fraction of the total occurs above the tropopause.
    watt : Unit of power, the rate of working of one joule per second, corresponding to an electric current where the electromotive force is one volt and the current one ampere.
    wavelength : the distance between successive peaks or troughs of a wave. It is equal to the velocity of the wave divided by its frequency. For electromagnetic radiation it is a parameter specifying the part of the electromagnetic spectrum to which the radiation belongs.
    wave number : the inverse of wavelength, i.e. the number of cycles executed by a wave in a unit length.
    wave theory of light : the model that depicts light as demonstrating all the properties of wave motion, analogous to waves on the surface of water.
    weak Sun paradox : referring to the fact that our sun has probably increased its luminosity during its lifetime (approximately 3.5 x 109 years). This assumption is based on astrophysical observations of many other stars. The best scientific conclusions are that when our sun was young it had a luminosity (total energy output) of 70-80% of what it is today; however, there has clearly been (based on geological records and long term evidence for the presence of liquid water) approximately the SAME long term planetary temperature on earth (about 15o C, averaged planet-wide) instead of colder earlier surface temperatures followed later by warmer surface temperatures. This paradox suggests that the planet's surface temperature may have been controlled by atmospheric gas concentrations that varied over time while keeping (via the greenhouse effect) the surface temperature relatively constant (see Gaia hypothesis).
    weber (wb) : the SI unit of magnetic flux equal to the flux linking a circuit of one turn that produces an electromotive force of one volt when reduced uniformly to zero in one second.
    wet bulb temperature (Tw) : an easily measurable quantity (using a sling psychrometer) which indicates the effect of evaporative cooling on temperature; used to determine relative humidity.
    white dwarf : a very small faint low-mass star (less than 1.44 solar masses) that has undergone gravitational collapse following exhaustion of its nuclear fuel. Electrons are stripped from the constituent atoms and it is the pressure exerted by these densely packed electrons that eventually halts the stars contraction. The density is hen 107 - 1011 kgm -3. As they cool their colours change from white (for the brightest) through yellow and red until they become cold black objects.
    wind shear : a changing of wind speed or direction with distance; vertical wind shear is changing of wind with respect to height.
    whorl : Arranged in radii around an axis, especially relevant in fingerprinting.
    Wolffian ducts : a pair of tubules which, in conjunction with mesonepheric ducts, form the primitive urogenital system of the male mammalian embryo. Both male and female embryos develop, though in females these ducts degenerate by the beginning of the third month.
    work : An indirect measure of the energy required to move matter a given distance.


    xenon (Xe) :
    xi ( X, x ) : fourteenth letter of the Greek alphabet.
    xylem : woody tissue at the stem of a plant that carries water and dissolved minerals upwards from the ground.
    xylene : an aromatic hydrocarbon used as a common industrial solvent, also named dimethylbenzene; exists as 3 isomers: m-xylene, o-xylene, and p-xylene. Xylene is usually obtained from petroleum and natural gas distillates. It is used in paint, rubber and leather industries, and also as a cleaning agent or degreaser.
    xylosyl :
    X-rays : Electromagnetic radiation lying between ultraviolet radiation and gamma rays in he electromagnetic spectrum. X-rays may have wavelengths between 10-9 m and 10-11 m, the shorter wavelengths being known as hard X-rays and the longer wavelengths as soft X-rays. They are produced when heavy atoms, usually tungsten, are struck by sufficiently energetic electrons, as in an X-ray tube. The electrons in an X-ray tube are produced by a heated cathode in a n evacuated tube and accelerated to the heavy metal anode by an electric field. The collisions knock inner electrons from the atoms. X-rays cause ionisation in gasses and penetrate matter.



    zenith : the point in the sky lying directly above the observer and 900 from all points on his horizon.
    zenithal hourly rate (ZHR) : This is the rate a meteor shower would produce if seen by an observer with a clear, dark sky, and with the radiant at the zenith.
    Zeolite : microporus silicate or aluminosilicate structured minerals that can act as an absorbing filter or sieve on a molecular level. Mainly used by the petroleum industry for the cracking of petroleum or use as a filter against various compounds.
    zeta (Z, z ) :
    zodiacal light : a faint glow that is visible in the western sky just after sunset and the eastern sky just before sunrise, especially in the tropics. It can be seen along the directions of the ecliptic, tapering upwards from the horizon to an altitude of up to 20o. It is the result of sunlight reflected from interplanetary dust particles.
    zonal : in the west-east direction.
    zonal sedimentation : An ultra-centrifugal technique in which the sediment in a solute is separated into discrete regions.
    zone focus : the ability to focus to a zone rather than a single point as in cameras that have fixed focus lenses. By retaining a large depth of field it is possible to cover all subjects with just one lens position.
    zoology : The study of animals.
    zwitterion : A molecule that can be either positively or negatively charged, depending on the pH.
    zygote : A diploid cell formed from the union of male (sperm) and female (egg) reproductive cells (gametes).