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1. Outline the classification and include living examples at all levels of classification.

Biologists classify algae into six divisions, based on color, foodstorage substances, and the composition of cell walls. Members of each division have distinctive colors, depending on the photosynthetic pigments in their cells. These pigments absorb light. All algae contain the pigment chlorophyll a. However, different divisions of algae also contain other forms of chlorophyll, such as b, c or d, each of which absorbs a different wavelength of light. Members of different algal divisions have different accessory pigments as well. Algae also vary in methods of reproduction.

Chlorophyta

Members of the Division Chlorophyta, the green algae, are a diverse group of organisms of over 7,000 species. They can be unicellular, colonial, filamentous, or thalloid. Most green algae are aquatic, although many inhabit moist terrestrial environments such as soil, rock surfaces and tree trunks.

Three observations have led biologists to conclude that green algae are the ancestors of plants. First, both green algae and plants have chloroplasts that contain chlorophyll's a and b. Second, both green algae and plants store food as starch. Finally, both green algae and plants have cell walls made of cellulose.

The diversity of unicellular algae is extreme. Chlamydomonas, a type of unicellular algae, is common in soils and in freshwater ponds and streams. It has a single-cup shaped chloroplast. Each chloroplast contains a pyrenoid, where starch is made. Two interior flagella enable the organism to swim. An eyespot, which is an area sensitive to light, enables the algae to move either toward or away from light. Desmids are unusual unicellular algae that live primarily in fresh water. In fact, the presence of desmids often indicates degree of water pollution. Each desmid cell is divided into half and these halves are called semicells.

Unlike unicellular algae, colonial algae have some characteristics of multicelluar organisms. Gonium is perhaps the simplest colonial algae, consisting of a colony that is one cell thick and shaped like a rectangle. A volvox colony, on the other hand, is round and much larger, containing up to 60,000 cells and exhibiting a remarkable division of labor. Intercellular communication allows the coordination of the many cells in the colony. Volvox cells are connected by fine cytoplasmic strands that enable adjacent cells to chemically communicate with each other.

Spirogyra is a filamentous green algae with unusual spiral chloroplasts that stretch from one end of the cell to the other. Oedogonium is another common freshwater filamentous green algae. members of this genus have netlike chloroplasts.

Ulva has a leaflike, photosynthetic body and commonly grows on rocks and pilings. Its thallus collapses during low tide to prevent water loss in the intertidal zone, the area between high and low tides.

Phaeophyta

Members of the Division Phaeophyta, the brown algae, are multicellular and usually large. Most of the approximately 1,500 species are marine organisms. Their brown color results from the accessory pigment fucoxanthin. The food they produce is stored as laminarin, a carbohydrate with glucose units linked different from those in starch.

Macrocystis are large brown algae and live in the intertidal zone. Individuals may be more than 100 m long. The thallus is composed of a holdfast, a stipe, and blades. The holdfast anchors the thallus to a rock. The stipe is the stemlike region. Each leaflike blade is a region modified for photosynthesis. The cell walls of these brown algae contain alginic acid, a source of commercially important alginates. Alginates are polysaccharides used to make gels for ice cream and other foods.

Rhodophyta

Members of the Division Rhodophyta are called red algae. Most of the approximately 4,000 species are marine and multicelluar. The multicellular forms are generally less then 1 m long. A few unicellular species inhabit land and freshwater environments. Red algae can survive at greater depths then any other algae can; they commonly grow at depths of 150 m and have been discovered in depths of 268 m. How can they photosynthesize at such depths? Red algae contain chlorophyll's a and d as well as accessory pigments called phycobilins. Phycobilins absorb violet, blue and green light that penetrates the depths at which these algae grow.

The cell walls of red algae contain cellulose and are sometimes coated with a sticky substance called carageenan. Carageenan, which is a polysaccharide, is used to produce cosmetics, gelatin capsules, and some cheeses. Coralline algae, a group of red algae that deposits calcium carbonate in their cell walls, are important components of coral reefs.

Chrysophyta

Members of the division Chrysophyta are called golden-brown algae. There are over 10,000 species of golden-brown algae, the majority of which are commonly called diatoms. Chrysophytes contain chlorophyll's a and c and the accessory pigment fucoxanthin. Because of the pigment similarities between golden-brown algae and brown algae, scientists suggest that the two divisions have a close evolutionary relationship. Chrysophytes store food in the form of oil, not starch.

Diatoms are unicellular or colonial, nonflagellated, photosynthetic algae with silica-impregnated shells. They inhibit both freshwater and marine environments and are an essential component of phytoplankton. Diatoms are so abundant in some marine environments that they are responsible for the bulk of worldwide photosynthesis.

Diatoms have highly ornamented double walls containing silicon dioxide. The two halves of the wall fit together like the two parts of a box. Each half is called a valve. Centric diatoms have circular or triangular valves and are most abundant in marine waters. Pennate diatoms have rectangular valves and are most abundant in freshwater ponds and lakes. Some pennate diatoms move by secreting threads that attach to the surface of water. When these threads contract, they pull the diatom forward.

Because their cell walls contain silicon dioxide, diatom shells do not decompose. Rather the rigid shells of dead diatoms sink and eventually form a layer of material called diatomaceous earth. Diatomaceous earth is slightly abrasive; it is an ingredient of many commercial products such as detergents, paint removers, fertilizers, and insulators.

Pyrrophyta

The approximately 1,100 species of the division Pyrrophyta are called fire algae, or dinoflagellates. Most dinoflagellates are marine and photosynthetic. Dinoflagellates are an important component of oceanic phytoplankton. The cell walls of dinoflagellates are made of cellulose. The cellulose forms plates that look like armor when seen under a microscope. The majority of cells are shaped like tops, but many have spinelike projections. Most dinoflagellates have two flagella that each fit into a groove in the cell wall. One groove runs vertically and is called a sulcus. The other groove runs horizontally and is called the girdle. Movement of the flagella causes dinoflagellate to spin like a top as it propels itself throughout the water.

Noctiluca exemplifies another characteristic of many dinoflagelates - the ability to produce light. Organisms that produce light are said to display bioluminescence.

Dinoflagellates are also responsible for a phenomenon known as red tide. Red Tides are discoloration's of sections of the ocean caused by population explosion of dinoflagellates such as Gonyaulax. During these population explosions, called algal blooms, the water appears red because of the pigments in the algae. Gonyaulax produces toxins that can cause respiratory paralysis in vertebrates. For example, if people eat mussels that feed on these toxic dinoflagellates, they may suffer a severe neurotoxic reaction called mussel poisoning, which has the potential to be fetal.

Euglenophyta

The approximately 1,000 species of the division Euglenophyta are unicellular algae with many features in common with green algae. However, they also have many characteristics similar to those of protozoa. Euglenoids contain chlorophyll's a and b and store food as starch, but they do not have cell walls. Unlike other algae, euglenoids are not completely autotrophic. If a euglenoid is placed in the dark, it will become heterotrophic. For these reasons some scientists classify euglenoids as protozoa.

The most familiar genus of euglenoids is Euglena, members of which are abundant in freshwater ponds and lakes. Euglena gracillis is generally elongate and fairly flexible. Like all species of Euglena, it is able to change shape because of the presence of a pellicle, a flexible proteinaceous covering. Euglena gracilis contains a structure called a reservoir with small openings that lead to the outside. A contractile vacuole is located in the reservoir. The contractile vacuole functions to rid the organism of excess water. Growing out of the reservoir and extending far beyond the cell is the long flagellum. A second flagellum is contained within the reservoir. Only the emergent flagellum moves the euglenoid about. A red-orange eyespot functions as a light detector and guides the photosynthetic algae toward bright areas.

2. Discuss the phylogeny and evolutionary status.

3. Describe the main characteristics displayed by the phyla. Show examples of how these characteristics are found among all the members of the phyla

Algae are a diverse group of eukaryotic, plantlike organisms. They are classified into six divisions of the Kingdom Protista. Algae are autotrophic protists - that is, they have chloroplasts and produce their own food by photosynthesis. In the past some biologists classified algae as plants. Today they do not. One reason is that algae and plants have different methods of reproduction. Algae have gametes that are formed in and protected by unicellular gametengia, or single celled gamete holders. Plants have gametes formed in multicellular gametangia.

Although algae form a very diverse group of protists, all algae have several features in common. For example, algal cells often have pyrenoids, organelles that synthesize and store starch. In addition, almost all algae are aquatic, and even terrestrial forms require H2O for reproduction. Many aquatic algae also posses flagella.

The body of an alga is called a thallus. The thallus can be unicellular, colonial, filamentous, or thalloid. Colonial algae are groups of independent cells that move and function as a unit. Filamentous algae consists of cells in a linear arrangement. Thalloid algae are organisms in which cells divide in many directions to create a body that is multicellular and often modified into rootlike, stemlike, or leaflike parts.

Unicellular algae are mostly aquatic. Organisms thus adapted are called plankton. Photosynthetic microorganisms are called phytoplankton. Phytoplankton provide food for numerous aquatic organisms. They also generate a great amount of oxygen we breathe.

Colonial algae are groups of individual algal cells. In colonies the algal cells act in a coordinated manner. Certain cells may become specialized for certain functions. This division of labor allows colonial algae to move, feed and reproduce efficiently.

A filamentous alga is composed of a row of cells. Some filamentous algae have structures that anchor them to the ocean bottom, where they can exploit an environment inhospitable to many other organisms. Some have branching filaments.

Multicelluar thalloid algae are not organized into specialized tissues but can often be very large and outwardly complex. Some algae grow as a complex thallus and are refereed to as seaweed's. For example Ulva, commonly known as sea lettuce, has a leaflike thallus that may be several centimeters wide but only two cells thick. Macrocystis, called the giant kelp, has a rubbery leaflike portion, stemlike areas and enlarged air bladders.

4. Explain in detail the reproductive patterns found in the phyla. How do these patterns increase the organisms ability to survive natural selection.

Some species of algae reproduce only asexually, thereby generating new organisms that are genetically identical with parent organisms. Other algae can reproduce either asexually or sexually. In these algae sexual reproduction is often triggered during periods of environmental stress.

Unicellular reproduction

Chlamydonas is a typical unicellular algae. Members of this genus reproduce by both sexual and asexual reproduction. During asexual reproduction Chlamydomonas first absorbs its flagella. The haploid cell then divides mitotically one to three times, and two to eight haploid, flagellated daughter cells called zoospores develop within the parent cell. These motile, asexual reproductive cells break out of the parent cell, disperse, land, and eventually grow to full size.

Sexual reproduction also begins when haploid cells divide mitotically to produce either plus or minus gametes. The plus and minus terminology is used when gametes look similar but differ in their chemical composition. A plus gamete and a minus gamete come into contact with one another and shed their cell walls. They fuse and form a diploid zygote, which develops a thick protective wall. A zygote in such a resting state is called a zygospore. The zygospore can withstand unfavorable environmental conditions. When conditions are favorable, the zygospore breaks out of the thick wall. It then divides by meiosis and forms typical haploid Chlamydomonas cells.

Diatoms also reproduce sexually or asexually. During asexual reproduction the two valves of the diatom shell split apart. Each valve then grows another valve within itself. This form of reproduction creates increasingly smaller diatoms However when it reaches a certain size a diatom sheds its shell, grows to a full size, regenerates its shell and begins the cycle again.

In sexual reproduction a diploid diatom undergoes meiosis to produce a gamete. Plus and Minus gametes unite to form a zygote that will grow into a mature diatom.

Multicellular reproduction

Reproduction of multicellular algae varies widely among the divisions. Reproduction in red and brown algae is very complex, with that of the red algae often involving three states in a sexual life cycle.

Conjugation : Spirogyra

Spirogyra, a filamentous green algae, reproduces sexually by a process called conjugation, in which one gamete moves to the other throughout a conjugation tube between adjacent filaments. First two filaments align side by side. The walls between adjacent cells then dissolve and a conjugation tube forms between the cells. One cell is considered to be a plus gamete. Its contents move throughout the conjugation tube, enter the adjacent cell, and fuse with the minus gamete. After fertilization the resulting zygote develops a thick wall, falls from the parent filament and becomes a resting spore. It later produces a new filament.

Egg and Sperm : Oedogonium

Oedogonium is another filamentous green alga. Oedogonium has cells specialized for producing gametes. The modified cells that reproduce and hold the gametes are called unicellular gametangia. The male unicellular gametangium is called an antheridium. It produces sperm. The female unicellular gametangium, the oogonium, produces an egg. Flagellated sperm are released from the antheridium into the surrounding water, swim to an oogonium, and enter throughout small pores. After fertilization the resulting zygote is released from the oogonium and forms a thick-walled resting spore. The diploid spore then undergoes meiosis, forming four haploid zoospores that are released into the water. Each zoospore settles and divides. One of the new cells will become an anchoring holdfast; the other will divide and form a new filament.

Alternations of generations: Ulva

The last form of multicellular algal reproduction that we’ll consider is the complex cycle known as alternation of generations. This cycle is characterized by two distinct multicellular phases: a haploid, gamete-producing phase called the gametophyte, and a diploid, spore producing phaser called the sporophyte.

If you take a Ulva which is a diploid sporophyte. The sporophyte forms reproductive cells called sporangia that produce haploid zoospores by meiosis. These zoospores divide mitotically, forming more motile spores. The spores settle throughout the water, land on rocks, and grow into multicellular , haploid gametophytes. A gametophyte looks exactly like the sporophyte. The gametophyte produces gametangia and then produces plus and minus gametes that unite and form zygotes. The diploid zygote completes the cycle by dividing mitotically into a new diploid sporophyte.

It is of exceptional significance that this life cycle occurs in a green algae. Plants, which presumably evolved from green algae, also have an alteration of generations as their sexual cycle. The plant life cycle differs from that of Ulva in two respects. The sporophyte and the gametophyte do not look alike, and gametes are formed in multicellular rather then unicellular gametangia.

5. Describe the relationship of these phyla with humans both positive and negative. Do they effect our survival?

Positive

Algae produce large quantities of oxygen

Algae is used as a food source

Algae is a basis for the sealife food chain

The cell walls of brown algae contain alginic acid, a source of commercially important alginates. Alginates are polysaccharides used to make gels for ice cream and other foods.

The cell walls of red algae contain cellulose and are sometimes coated with a sticky substance called carageenan. Carageenan, which is a polysaccharide, is used to produce cosmetics, gelatin capsules, and some cheeses. Coralline algae, a group of red algae that deposits calcium carbonate in their cell walls, are important components of coral reefs.

Diatoms a type of algae has many uses in our world:

Because their cell walls contain silicon dioxide, diatom shells do not decompose. Rather the rigid shells of dead diatoms sink and eventually form a layer of material called diatomaceous earth. Diatomaceous earth is slightly abrasive; it is an ingredient of many commercial products such as detergents, paint removers, fertilizers, and insulators.

Negative

Dinoflagellates of the division Pyrrophyta are responsible for a phenomenon known as red tide. Red Tides are discoloration's of sections of the ocean caused by population explosion of dinoflagellates such as Gonyaulax. During these population explosions, called algal blooms, the water appears red because of the pigments in the algae. Gonyaulax produces toxins that can cause respiratory paralysis in vertebrates. For example, if people eat mussels that feed on these toxic dinoflagellates, they may suffer a severe neurotoxic reaction called mussel poisoning, which has the potential to be fetal.

 

6. Explain something you found interesting about these organisms.

I thought that members of the division Euglenophyta were very interesting because they can be heterotrophs in the dark.

The approximately 1,000 species of the division Euglenophyta are unicellular algae with many features in common with green algae. However, they also have many characteristics similar to those of protozoa. Euglenoids contain chlorophyll's a and b and store food as starch, but they do not have cell walls. Unlike other algae, euglenoids are not completely autotrophic. If a euglenoid is placed in the dark, it will become heterotrophic. For these reasons some scientists classify euglenoids as protozoa.

The most familiar genus of euglenoids is Euglena, members of which are abundant in freshwater ponds and lakes. Euglena gracillis is generally elongate and fairly flexible. Like all species of Euglena, it is able to change shape because of the presence of a pellicle, a flexible proteinaceous covering. Euglena gracilis contains a structure called a reservoir with small openings that lead to the outside. A contractile vacuole is located in the reservoir. The contractile vacuole functions to rid the organism of excess water. Growing out of the reservoir and extending far beyond the cell is the long flagellum. A second flagellum is contained within the reservoir. Only the emergent flagellum moves the euglenoid about. A red-orange eyespot functions as a light detector and guides the photosynthetic algae toward bright areas.

7. Make a running list of all organisms for each phyla you observe in class.

Red Algae : Kallimenia reniformis, Scinaia furcellata

Unicellular green alga : Chlamydomonas

Colonial algae: Pandorina colony, Pleodorina colony, gonium, Eudorina, Volvox

Multicellular green algae : Ulothrix, Stigeooclonium