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Chapter 14
1. F
2. T
3. T
4. T
5. T
6. F
7. T
8. T
9. T
10. T
11. d
12. d
13. d
14. c
15. a
16. c
17. d
18. a
19. a
20. b
21. d
22. c
23. c
24. d
25. d
26. c
27. d
28. c
29. b
30. d
31. d
32. b
33. d
34. c
35. d
36. c
37. a
38. b
39. b
40. d
41. d
42. grasping
43. binocular
44. prosimians
45. diurnal
46. opposable
47. Hominids
48. Lucy
49. mitochondrial
50. Neander
51. Homo Habilis
52. Peking
53. Homo sapiens
54. Scientists have started looking at mitochondrial DNA to study evolution since the DNA of the mitochondria is only transmitted by females. It is possible to trace genetic variations within a mitochondrial gene back through a family tree, from mother to grandmother to great-grandmother. Since DNA accumulates mutations (changes in genes) over time, the oldest mitochondrial DNA should show the largest number of mutations. It turns out the greatest number of different mitochondrial DNA sequences occurs among modern Africans. The results from the DNA studies indicate that Homo sapiens have been living in Africa longer than on any other continent. While there is no yet universal agreement among researchers, this evidence supports the hypothesis that Homo sapiens evolved first in Africa. If this is true, the varieties of living humans evolved after that, and not independently from separate populations of Homo erectus. This would mean our species was born in Africa and spread from there to all parts of the world. Results from nuclear gene research agree with the mitochondrial study findings. Indeed, it seems that Homo sapiens retraced the path taken by Homo erectus half a million years earlier.
55. Rare at first outside of Africa, Neanderthals became progressively more abundant in Europe and Asia, and by 70,000 years ago they had become common. Neanderthals took care of their injured and sick and commonly buried their dead, often placing food, weapons, and even flowers with the bodies. This is typical of human burial and hospitals in the modern day take care of the injured. Modern humans such as in Egypt also had a strong belief in the afterlife and placed material possessions with the dead. Such attention to the dead suggest that they too believed in a life after death. The Neanderthals were the first hominids to show evidence of the abstract thinking characteristic of modern humans.
56. Our evolution has been marked by a regular increase in brain size. Our ability to make and use tools effectively is a capability that has, more than any other, been responsible for our dominant position in the animal kingdom. Humans use symbolic language and can shape concepts out of experience. Language has allowed us to transmit accumulated experience from one generation to another. Thus, humans have what no other animal has ever had—cultural evolution. Through culture, we have found ways to change and mold our environment to our needs, rather than changing ourselves in response to the future in a way never before possible. Intelligence is the result of brain size and due to this humans are able to have conceptual thinking. Humans can also protect themselves from the nature, diseases, and so on; they can also accumulate resources due to their intelligence. Intelligence is a big factor in evolution and survival.
57. b
58. a
59. d
60. e
61. c
62. c
Chapter 15
1. T
2. F
3. T
4. T
5. F
6. T
7. F
8. F
9. T
10. F
11. c
12. a
13. b
14. d
15. d
16. a
17. d
18. d
19. c
20. b
21. b
22. c
23. d
24. d
25. b
26. d
27. c
28. c
29. b
30. b
31. b
32. c
33. c
34. d
35. population
36. demography
37. individuals
38. dispersion
39. microhabitats
40. model
41. Rate of growth
42. carrying-capacity
43. r-strategists
44. K-strategists
45. K-strategists
46. alleles
47. allele frequencies
48. migration
49. genetic polymorphism
50. polygenic
51. Stabilizing
52. R-strategists may include bacteria, some annual plants and insects which asexually reproduce while K-strategists are such large animals as redwood trees, whales, and rhinoceroses. K-strategists have small population sizes and slow population growth while r-strategists grow exponentially which is fast, and have temporarily large populations but which are followed by sudden crashes as they reach the environments carrying capacity. K-strategists are characterized by a high degree of specialization. R-strategists live in unpredictable and rapidly changing environments, where when conditions are favorable, it pays to reproduce quickly. K-strategists live in environments which are stable and predictable where they are able to compete effectively. K-strategists reproduce late in life and have few offspring when they reproduce, whereas r-strategists reproduce early in life and have many offspring. K-strategist offspring are large, mature slowly, and receive extensive parental care but r-strategists’ offspring are small, mature rapidly, and receive little or no parental care which is the opposite. In r-strategists the parent invests in many offspring and little into each individual one. K-strategists are in danger of extinction due to their slow reproductive habits, such as the tiger.
53. First, calculate the frequency of the recessive allele, since 16 out of 100 birds have the recessive genetic disorder, q2=0.16. Take the square root of that and you figure out that q=0.4. Second, calculate the frequency of the dominant allele. Because p+q=1, p=1-q. So p=1-0.4, then p=0.6. Finally you are ready to determine the frequency of heterozygous which would be 2pq. Since p=0.4 and q=0.6, then 2pq=0.48. So the frequency is 0.48. This means that 48 out of 100 of the bird population are heterozygous carriers.
54. The three forms of natural selection acting on polygenic traits are directional selection, stabilizing selection, and directional selection. Directional selection is selection against one extreme form of a polygenic trait such that the average value is shifted toward the other extreme. Stabilizing selection is selection against both extremes of a polygenic traits, so the average value does not change, but becomes more narrow and is intermediate. Disruptive selection is selection against intermediate polygenic traits, shifting the population to exhibit the two extremes.
55. b
56. c
57. a
58. a
59.d
60. c
61. e
62. c
63. a
64. c
65. d
Chapter 16
1. T
2. F
3. F
4. T
5. F
6. T
7. T
8. F
9. F
10. F
11. F
12. T
13. F
14. T
15. a
16. d
17. c
18. c
19. d
20. c
21. b
22. a
23. b
24. b
25. b
26. c
27. d
28. a
29. a
30. b
31. b
32. b
33. b
34. c
35. c
36. d
37. a
38. d
39. d
40. d
41. c
42. c
43. d
44. non-living
45. detritivores
46. food chain
47. heat
48. biomass
49. photosynthetic
50. trophic
51. food web
52. ground
53. transpiration
54. proteins
55. nitrification
56. assimilation
57. dentrification
58. It is cheaper for a farmer to produce a pound of grain than a pound of meat because of the energy transfer in the ecological pyramid. Grain is a producer and is made by the energy from the sun while meat would be from a cow, or some other animal which are consumers and herbivores. Only 10% of the energy is passed on to the herbivorous animal and the rest is dissipated into heat, wastes, etc.. So it takes 10 pounds of grain to feed the herbivores animal to produce one pound of meat, while the same amount of energy is contained in 1 pound of grain. Therefore you have to produce a lot more grain to raise such animals as cows. The grass, or grain that they eat is 10 times more than what the farmer gets.
59. When an animal such as a deer eats leaves, it is acquiring energy. The energy is stored within the chemical bonds of the food that the animal eats. Once it is consumed some of it is transferred to other forms of potential energy such as fat. Another portion accomplishes mechanical work such as running, breathing, and eating more leaves. However, almost ½ of the energy is dissipated to the environment as heat. Every transfer within an ecosystem dissipates energy as heat, which is not a useful source of energy for biological organisms. The amount of useful energy available to do work decreases as energy passes through an ecosystem. The loss of useful energy to heat limits the amount of trophic levels in an ecosystem. When a plant harvests energy from sunlight to make structural molecules such as cellulose, it stores in chemical bonds on about one-half of the energy it is able to capture, losing the rest as heat. This is the first loss of the energy transfer. When a herbivore uses plant molecules to make its own, only about 10% of the energy of the previous molecules ends up in the herbivores molecules, 90% is lost. And when the carnivore eats the herbivore, 90% of the energy that remains is lost to making the carnivores molecules. At each trophic level, the energy stored by the organisms is about one-tenth of that stored by the organisms in the level below.
60. Decomposers are necessary for the continuation of life on the earth because they cause decay so they release nutrients back into the environment to be used by other organisms. So other forms of life get the nutrients as they are recycled. Decomposers play a critical role in the nitrogen cycle as bacteria are the only organisms that can break down the triple covalent bond of N2 in nitrogen fixation. Bacteria(decomposers) help recycle the nitrogen such that the cycle can continue and so can life.
61. The flow of matter and the flow of energy throughout an ecosystem have much in common. The energy path is who eats whom. The energy is spread by organisms through trophic levels. This is very inefficient because so much energy is lost at each trophic level. The movement of matter is similar to that of energy in that it cycles through the environment, like the water cycle. Unlike the flow of energy, it is far more efficient, because not much material is lost. Biomass decreases at each trophic level as energy does and also forms a pyramid of biomass like a pyramid of energy. Energy is lost at each level and eventually completely but matter such as nitrogen and water tends to cycle through an ecosystem.
62. c
63. b
64. c
65. c
66. b
67. e
68. a
Chapter 17
1. F
2. F
3. F
4. T
5. T
6. F
7. F
8. F
9. T
10. F
11. F
12. c
13. a
14. c
15. c
16. d
17. b
18. b
19. c
20.
21. d
22. d
23. c
24. d
25. c
26. d
27. d
28. a
29. a
30. a
31. b
32. c
33. d
34. c
35. c
36. b
37. b
38. c
39. competition
40. predation
41. coevolution
42. commensalism
43. carnivore
44. niche
45. competitive exclusion
46. fundamental niche
47. solar
48. low
49. Savanna
50. Taiga
51. No, they can not occupy the same niche. To prove this, we have to look into the experiment of G. F. Gause who took two species of the protist Paramecium and put them in culture tubes were they had to compete for the same resource. Invariably, the smaller of the two species which was more resistant to bacterial waste products, drove the larger one to extinction. From this he got the principle of competitive exclusion. This principle states that if two species are competing, the species that uses the resource more efficiently will eventually eliminate the other locally – no two species can have the same niche.
52. Because the earth is nearly spherical, different places on the surface receive different amounts of solar energy. These differences are directly responsible for many of the major climatic differences that occur over the Earth’s surface and indirectly responsible for much of the variety of ecosystems. At regions near he equator, the sun’s rays arrive almost perpendicularly, making the tropics warmer than the temperate regions. Nearer the poles, the angle at which the sun’s rays hit the Earth spreads them out over a much greater area, providing less energy per unit of area.
53. When mountains force incoming air upward, the air’s moisture-holding capacity decreases as the air cools, resulting in increased precipitation on the windward side (from which the wind is blowing) of the mountains. As the air descends the other side of the mountains, known as the leeward side, it is warmed, and its moisture-holding capacity increases. Therefore, it tends to draw up moisture from the surface, rather than releasing the little moisture it contains. The leeward sides of mountains are often much drier than their windward sides, and the vegetation is often very different. This phenomenon is called the rain-shadow effect. In the United States, the Mojave and Great Basin Deserts lie in the rain shadow of the Sierra Nevada range, and the Great Plains lie in the rain shadow of the Rocky Mountains.
54. b
55. d
56. e
57. e
58. a
59. d
60. c
61. c
62. e
Chapter 18
1. F
2. F
3. F
4. T
5. F
6. T
7. T
8. F
9. F
10. F
11. F
12. T
13. d
14. a
15. b
16. d
17. d
18. d
19. c
20. a
21. b
22. b
23. b
24. a
25. d
26. b
27. b
28. d
29. d
30. c
31. b
32. d
33. a
34. d
35. b
36. a
37. d
38. a
39. d
40. ultraviolet
41. green house effect
42. oxygen
43. nonreplacable
44. death
45. 12,000
46. aquifers
47. 6
48. developing
49. Assessment
50. pollution permit
51. sulfur dioxide
52. supply
53. chemicals
54. Sulfur is introduced to the atmosphere by smokestacks from a plant which burns coal. Coal is rich in sulfur so burning it lets it of into the atmosphere. The sulfur combines with water vapor to produce sulfuric acid. Rain and snow carry the sulfuric acid back to the surface. This acidified precipitation is called acid rain.
55. To learn what must be done, it is first necessary to understand the ultimate cause of pollution. In essence, it is a failure by our economy to set an appropriate value on environmental health. To understand how this happens, you must think for a moment about money. The economy of the United States (and much of the rest of the industrialized world) is based on a simple feedback system of supply and demand. As something gets scarce, its price increases. This added profit acts as an incentive for the production of more of the item. If too much of the item is available, the price falls, and because it is no longer so profitable to produce the item, less of it is made. This system works very well and is responsible for the economic strength of our nation. But it has one great weakness: if demand is set by price, then it is very important that all of the costs be included in the price. Imagine if the person selling the item is able to pass off part of the production cost to a third person; the seller would be able to set a lower price and sell more of the item, And, stimulated by the lower price, the buyer would purchase more than if all the costs had been added into the price. That sort of pricing error is what has driven industry’s pollution of the environment over the last century. The true costs of energy and of the many things made by industry are composed of direct production costs, such as materials and wages, and indirect costs, such as pollution and the risk of unanticipated ill effects to the environment. Imagine if all the medical costs associated with a 20% worldwide increase in skin cancer were factored into the price of a refrigerator or air conditioner (because of the ozone-destroying CFCs they contain). Indirect costs from the use of fossil fuels include reduced harvests of fish and shellfish due to oil spills, and crop and timber losses cause by air pollution. Pollution from fossil fuels also damages building and causes illness and death. Since the indirect costs are not included in the price that the consumer pays, far more is consumed than if they had been included. By not adding the indirect costs to the price of energy and manufactured goods, our society has made it profitable to pollute. The indirect costs do not disappear because we ignore them; they are simply passes on to future generations, who must pay the bill in terms of damage to their own health and to the ecosystems on which they depend.
56. Assessment- The first stage of addressing any environmental problem is scientific analysis, the gathering of information about what is happening. Data must be collected and experiments must be performed to construct a model of the ecosystem that describes how the ecosystem is responding to the situation. Such a model can then be used to make predictions about the future course of events in the ecosystem.
Risk Analysis- Using the information obtained by scientific analysis, it is possible to predict the consequences of environmental intervention—what could be expected to happen if a particular course of action were followed. It is necessary to evaluate not only the potential for solving the environmental problem, but also any adverse effects that a plan of action might create.
Public Education- When a clear choice can be made among alternative courses of action, the public must be informed. This involves explaining the problem in understandable terms, presenting the alternative action available, and explaining the probable costs and results of the different choices
Political Action- The public, through its elected officials, selects and implements a course of action. Individuals can have a major impact at this stage by exercising their right to vote and by contacting their elected officials. Many voters do not realize how much they can achieve by writing letters and supporting special interest groups.
Follow-through- The results of any action should be carefully monitored to see if the environmental problem is being solved, The results can also be used to evaluate and improve the initial assessment and model of the problem. We learn by doing.
57. c
58. b
59. e
60. a
61. c
62. d
63. b
64. e
65. a
66. b
Chapter 19
1. F
2. T
3. F
4. T
5. F
6. T
7. T
8. F
9. T
10. F
11. T
12. F
13. a
14. d
15. d
16. b
17. c
18. c
19. b
20. d
21. d
22. d
23. d
24. d
25. c
26. c
27. c
28. d
29. b
30. d
31. c
32. a
33. d
34. b
35. c
36. d
37. c
38. b
39. peptidoglycan
40. gametic
41. sporophyte
42. aggregation
43. specialization
44. Latin
45. taxonomy
46. hybrids
47. division
48. phylogeny
49. Animalia
50. Plantae
51. Protista
52. Fungi
53. To explain the origins of mitochondria, most biologists accept the theory of endosymbiosis. The theory of endosymbiosis, proposes that mitochondria are the descendents of symbiotic, aerobic eubacteria. The symbiotic bacteria may have first entered large cells (similar to Pelomyxa) as parasites or undigested prey and eventually taken up residence there. The eubacteria most similar to mitochondria are the nonsulfur purple bacteria, which are able to carry out the key metabolic process of oxidative respiration. Before they had acquired these bacteria, the larger host oxidative respiration, a process essential for living in an atmosphere that contained increasing amounts of oxygen. These observations support the idea:
1. Size and Structure- Mitochondria are sausage-shaped organelles 1-3µm long, about the same size as most eubacteria. They are bound by two membranes. The smooth outer membrane is thought to be derived from the endoplasmic reticulum of the larger host cell. The inner membrane is folded into numerous layers, resembling the plasma membranes of aerobic eubacteria. Embedded within this membrane are proteins that carry out oxidative respiration.
2. Genome- Mitochondria have DNA in the form of a circular, closed molecule similar to the chromosome found in bacteria. This DNA molecule contains the genes encoding the essential proteins of oxidative respiration. However, during the billion and half years in which mitochondria have existed within eukaryotic cells, most of their genes have been transferred to the chromosome of host cells.
3. Gene translation machinery- Genes within mitochondrial DNA are expressed within mitochondria, Mitochondrial ribosome’s resemble bacterial ribosome’s in size and structure.
4. Reproduction- Mitochondria, like bacteria, reproduce by simple fission. However, genes in the cell nucleus direct mitochondrial reproduction.
54. In order to name the insect, you must go through a process which every organism goes through when being names. Since you already know it is an insect, it belongs to the class insecta, phylum arthropoda, and kingdom animalia. You decide the order by the properties of the insect. You decide the family by more specific properties. Then you decide the genus, if a genus does not exist for the particular plant, you make one. The species is decided by yourself who names it. The scientific name is two words, first one genus, and the second one species. The name has to be descriptive and in Latin.
55. Although a horse and a donkey can mate, they are not the same species because their offspring, a mule, is sterile. For a horse and a donkey to be the same species they must be able to interbreed and produce fertile offspring. The mule is sterile so horses and donkeys are not the same species. Their offspring, a mule, is a hybrid.
56. Peloxyma is a single-celled, nonphotosynthetic organism found on the bottom of freshwater ponds. Like some of the early eukaryotes, Pelomyxa is much larger than a prokaryotic cell and contains a complex system of internal membranes. It also resembles some of the fossils of early eukaryotes. However, Pelomyxa still resembles bacteria in two ways. First, it does not have mitochondria, the sites of cellular respiration in eukaryotic cells. However, it does contain two kinds of bacteria that may play the same role that mitochondria do in all other eukaryotes. Second, Pelomyxa does not undergo mitosis like eukaryotic cells. Instead, its nuclei divide in a manner similar to binary fission in bacteria: they divide by pinching apart into two new nuclei around which members form. Many of the fundamental characteristics of Pelomyxa resemble those of the archeabacteria far more than those of the eubacteria.
57. b
58. e
59. d
60. a
61. d
62. b
63. c
64. b
65. d
Chapter 20
1. F
2. T
3. T
4. T
5. F
6. F
7. F
8. F
9. T
10. T
11.d
12. c
13. d
14. c
15. b
16. d
17. a
18. b
19. c
20. c
21. b
22. d
23. a
24. c
25. c
26. d
27. d
28. d
29. a
30. b
31. d
32. d
33. a
34. c
35. c
36. d
37. c
38. a
39. c
40. d
41. b
42. a
43. a
44. b
45. d
46. viruses
47. Tobacco Mosaic Virus
48. capsid
49. bacteriophage
50. pathogens
51. antibody
52. reverse transcriptase
53. retrovirus
54. bacilla
55. coccus
56. spirillum
57. peptidoglycan
58. endospores
59. autotrophic
60. heterocysts
61. chemoautotrophic
62. nitrification
63. Tuberculosis
64. Antibiotic
65. E. coli
66. Biologists do not consider viruses to be living organisms. They are incorporated into biology due to the tremendous effect they have on living organisms. They infect cells by getting and overtaking the cell’s machinery and in most cases, kill the person they infect. They reproduce and there are more viruses and they spread through the body much like cancer, out of control cell division. Viruses even originated as fragments of bacterial and eukaryotic genomes and their diversity is great. There are also a lot of types of viruses, much like species in organisms
67. Eubacteria are commonly classified by differences in their cell walls. A bacterium with a cell wall containing a large amount of peptidoglycan is classified as gram-positive. A bacterium with a cell wall containing a thin layer of peptidoglycan covered by an outer membrane classified as gram-negative. These terms refer to a bacterium’s reaction to a staining procedure developed by the Danish microbiologist Hans Gram. In this procedure, a sample of bacteria is covered in a series of chemicals, beginning with a purple dye that stains the cell wall and ending with an alcohol rinse that breaks down cell membranes. Gram-positive bacteria retain the purple dye because their thick peptidoglycan layer remains intact and prevents the dye from leaving the cell. Gram-negative bacteria are not stained purple because the outer membrane is removed by the alcohol rinse and their thin peptidoglycan layer allows the dye to escape the cell. Gram-negative bacteria are usually identified by a pink stain that is applied after the alcohol wash.
68. Penicillin is an example of an antibiotic, a substance obtained from bacteria or fungi that is used as a drug to fight pathogenic microorganisms. Antibiotics work by interfering with the microorganism’s cell8ular processes. In most cases, this includes preventing cell wall formation, breaking up cell membranes, or disrupting chemical processes. Because these processes do not occur in viruses, antibiotics cannot be used for fighting viral diseases. Antibiotics work on living bacteria cells, and since virus’s are not living, they do not work.
69. d
70. b
71. d
72. b
73. d
74. e
75. b
76. c
77. d
Chapter 21
1. F
2. F
3. F
4. F
5. F
6. F
7.T
8. F
9. T
10. T
11. T
12. F
13. b
14. d
15. d
16. c
17. c
18. b
19. b
20. d
21. a
22. a
23. c
24. c
25. b
26. d
27. d
28. d
29. d
30. c
31. a
32. c
33. b
34. a
35. b
36. multicellularity
37. stress
38. eyespots
39. tests
40. pellicle
41. dinoflagelliates
42. bilateral
43. sporozite
44. protists
45. psudopod
46. cilia
47. flagella
48. asexually
49. zoospore
50. zygote
51. conjugation tube
52. Some zoomastigotes such as Trichonympha, live symbolically in the guts of termites, where they provide the enzymes that digest wood. Trichonympha is a protist that inhabits the digestive tracts of termites, where it aids in digesting cellulose. Rows of flagella protrude from one end of the cell.
53. Euglenoids, members of the phylum Euglenophyta are freshwater protists with two flagella. They clearly illustrate the impossibility of classifying protists as animals or plants. About one-third of the 1,000 known species of euglenoids have chloroplasts and are photosynthetic; other species lack chloroplasts, ingest their food, and are heterotrophic. Some photosynthetic euglenoids may reduce the size of their chloroplasts and become heterotrophic if they are kept in a dark environment. If they are put back in the light, their chloroplasts return to normal size within a few hours, and photosynthesis resumes.
54. The symptoms of malaria include severe chills, fever, sweating, confusion, and great thirst. The malaria sporozoan parasite is Plasmodium, which is spread by mosquitoes. Mosquitoes inject a substance with saliva which prevents blood from clotting and injects 1,000 elongated cells. There are three stages in the Plasmodium life cycle. The stage of Plasmodium while it lives in mosquitoes and is injected is sporozoite, which make their way through the blood stream to the liver in about three minutes. In the liver, they rapidly divide and produce millions of cells of the second stage of the life cycle, called the merozoite. Merozoites reenter the host’s bloodstream, invade red blood cells, and divide rapidly. In about 48 hours the blood cells rupture, releasing merozoites and toxic substances throughout the host’s body, initiating a cycle of fever and chills that characterizes malaria. The cycle repeats itself regularly every 48 hours as new waves of blood cells are infected. Because of these symptoms, the doctor suspects malaria.
55. d
56. e
57. b
58. a
59. d
60. b
61. c
62. d
Chapter 22
1. F
2. F
3. T
4. F
5. T
6. F
7. F
8. T
9. T
10. F
11. T
12. c
13. b
14. b
15. d
16. d
17. b
18. c
19. d
20. b
21. b
22. b
23. d
24. d
25. d
26. d
27. d
28. a
29. a
30. a
31. a
32. c
33. d
34. d
35. c
36. b
37. d
38. asexually
39. mycelium
40. decompose
41. ascomycota
42. spore
43. yeast
44. basidum
45. ascomycetes
46. ascus
47. alga
48. pollution
49. ectomycorrhizae
50. nitrogen
51. Mitosis in the mushroom is different from that in most other eukaryotic organisms, in which the nuclear envelope disintegrates in prophase and re-forms in telophase. In dividing mushroom cells, by contrast, the nuclear envelope remains intact from prophase to anaphase. Consequently, spindle fibers from within the nucleus, dragging chromosomes to opposite poles of the nucleus, not opposite poles of the cell. Mitosis is completed when the nuclear envelope pinches into two.
52. If a fungus is growing on an orange, the green and white fuzz you recognize as mold is actually the reproductive structures of the fungus. The body of the fungus lies woven within the tissues of the orange. All fungi except yeast’s have bodies composed of slender filaments called hyphae. When hyphae grow, they branch and form a tangled mass called a mycelium. A mycelium can be made of many meters of individual hyphae. This body organization creates a high surface-area-to-volume ration, which makes a fungus well suited for absorbing food from the environment. Each hyphae is a long string of cells divided by walls called septa. In most kinds of fungi, septa do not form a complete barrier between cells. From one cell to the next, cytoplasm flows freely throughout the hyphae through perforations in the septa. Other organelles, such as ribosome’s, mitochondria, and nuclei, also pass through these perforations. A typical fungal cell usually has many nuclei streaming in the cytoplasm.
53. Lichens are extremely sensitive to pollutants in the atmosphere because they readily absorb substances dissolved in rain and dew. Pollutants such as sulfur dioxide, a byproduct of automobile engine exhaust and industrial activity, quickly destroy a lichen’s chlorophyll, decreasing its rate of photosynthesis. As a result, the physiological balance of the symbiotic relationship is upset. For this reason, lichens do not grow in or around cities. Biologists use the relative health of lichens and their chemical compositions as indicators of an environment’s health. Recently, biologists have discovered that lichens are disappearing from national parks and other remote areas, which, despite their distance from the sources of pollution, are clearly being affected by the quality of air that reaches them.
54. In the mycorrhizae of most species of plants, the fungal hyphae penetrate the outer cells of the root and form coils, swellings, and tiny branches that extend into the surrounding soil. These are called endomycorrhizae. The fungus involved is usually a zygomycete. Fossils reveal that the rootlike appendages of the earliest plants often had endomycorrhizae, which may have played an important role in the invasion of land by plants. The soil of that time was completely lacking in organic matter, and mycorrhizal plants are particularly successful in infertile soil, Some archaic primitive vascular plants surviving today continue to depend strongly on endomycorrhizae.
55. b
56. d
57. a
58. d
59. e
60. b
61. c
62. c
63. c
There, aren’t you glad you did not have to do this annoying, and long test!
