ALGAE Algae Are Photosynthetic Eukaryotes with a Wide Variety of Shapes That Occur in Most Habitats, Ranging from Marine And

ALGAE Algae are photosynthetic eukaryotes with a wide variety of shapes that occur in most habitats, ranging from marine and freshwater to desert sands and from hot boiling springs to snow and ice belonging to Kingdom Protista. Algae vary from small, single-celled forms (filamentous) to most complex multicellular forms. They are not plants, they are more plantlike than protozoa. Algae lack true roots, stems and leaves. They important role in balancing the environment. They reproduce sexually and asexually. They are photoautotrophic, as photosynthesizer, algae need light and air for food production and growth, but do not generally require organic compounds from the environment. As a result of photosynthesis, algae produce oxygen and carbohydrates which are utilized by other organisms. Depending on the type of photosynthetic pigments they possess, they are classified as green, golden, brown or red. Algae are important as primary producers of organic matter at the base of the food chain. They also provide oxygen for other aquatic life. Algae may contribute to mass mortality of other organisms, in cases of algal blooms, but they also contribute to economic well- being in the form of food, medicine and other products. In tropical regions, coralline algae can be as important as corals in the formation of reefs. Seaweeds are larger algae that live in the marine (salt or brackish water) environment. Kelps are large brown seaweeds in the genera Pelagophycus, Laminaria, Macrocystis, etc. In the Pacific, individual kelp plants may reach 65 meters in length. CHARACTERISTICS OF ALGAE Algae are simple eukaryotic photoautotrophs. Most are found in the ocean. Algae can be unicellular or multicellular. 1. Vegetative structures—the body of a multicellular alga is called a thallus. This would include such algae as seaweed. The thalli consist of branched holdfasts to anchor the algae in place, stemlike stipes and leaflike blades. The cells covering the thallus carry out photosynthesis, and algae also can absorb nutrients from the water. Some algae are buoyed by a floating, gas-filled bladder called a pneumatocyst. 1 2. Life Cycle—all algae can reproduce asexually. Multicellular algae can fragment. Unicellular algae divide by mitosis and cytokinesis. Some algae also reproduce sexually. In some of these asexual reproduction is most common and sexual reproduction only occurs under special conditions. Other species alternate, reproducing asexually and then sexually in alternating generations. 3. Nutrition—almost all algae are photoautotrophs and are found in the photic (light) zone in bodies of water. Chlorophyll and sometimes other pigments are responsible for the colors of algae and their ability to carry out photosynthesis. DIFFERENT PHYLA OF ALGAE Algae are classified according to their rRNA, structures, pigments, and other qualities. 1. Phaeophyta or Brown algae - also known as kelp, are macroscopic and may reach lengths of 50 meters. Most are found in coastal waters and grow very rapidly. Algin, a thickener used in foods such as ice cream, is extracted from the cell walls. This product is also used in hand lotion. 2. Rhodophyta or Red algae - these live deeper in the ocean than other algae. Agar is extracted from them. Another product, carageenan, comes from a species of red algae known as Irish moss and is used as a thickening agent in evaporated milk, ice cream and drugs. Some of these produce a lethal toxin. Used in extracts of ―carageenan‖ and ―agar‖, Gracilaria spp.- as a food source 3. Chlorophyta or Green algae— Most green algae are microscopic, and may be either unicellular or multicellular. Most green algae have firm cell walls composed of cellulose along with other polysaccharides and proteins; store starch. Green algae may have given rise to terrestrial plants. Some form grass-green scum in ponds. 2 Most chlorophytes are aquatic, but some green algae can live on the surface of snow, on tree trunks, in soils, or symbiotically with protozoans, hydras or lichen-forming fungi. The typical color of plants in the Chlorophyta, resulting from the dominant chlorophyll pigments, is some shade of apple or grass green, although certain species may appear yellow-green or blackish-green due to the presence of carotenoid pigments or high concentrations of chlorophyll. Chlorophytes appear more than a billion years ago in the fossil record. These includes Desmids, Spirogyra, Chlamydomonas, Volvox, Euglena which are found in pond water a. Desmids – unicellular algae, resemble microscopic banana Desmids b. Spirogyra – filamentous algae, producing long green strands Spirogyra 3 c. Chlamydomonas – unicellular, biflagellated alga, containing one chloroplast and a stigma. Flagellated Chlamydomonas d. Volvox – multicellular alga, also known as “colonial alga”, biflagellated cells arranged to form a hollow sphere. Volvox e. Euglena – feature possess both alga and protozoa. It contains chloroplasts, photosynthetic and stores energy in the form of starch - possesses stigma (photosensing organelle), single flagellum (for motility), pellicle (protection) - protozoan features include the presence of ―cytostome” (primitive mouth) and absence of cell wall. Euglena 4. Bacillariophyta or Diatoms—unicellular or filamentous algae with complex cell walls that consist of pectin and silica that are important components of phytoplankton as primary sources of food for zooplankton in both marine and freshwater habitats. Most diatoms are planktonic, but some are bottom dwellers or grow on other algae or plants. Some produce a toxin called domoic acid, which can affect people, marine mammals, and birds that eat mussels that have fed on diatoms. Deposits are used to make diatomaceous earth, used in filtration systems, insulation and abrasives. 4 Marine Diatoms Diatoms 5. Dinophyta (Dinoflagellates)— microscopic, unicellular, flagellated and photosynthetic algae called plankton. Dinoflagellates produce much oxygen in our atmosphere and important links in food chain. They produce light sometimes referred as ―fire algae‖. They have cellulose embedded in the plasma membrane. Some produce neurotoxins which may affect fish, marine mammals, and humans who eat mollusks such as mussels and clams. Large concentrations of one toxic genus, Alexandrium, give the ocean a red color and are called red tides. The neurotoxin involved causes paralytic shellfish poisoning. A disease called ciguatera occurs when the toxin of the dinoflagellate Gambierdiscus toxicus is concentrated in fish. Figure 1.2.10: Flagellates, Dinophysis Figure 1.2.11: Dinoflagellate Red tide 5 6. Oomycota (water molds)—once classified as fungi, they are now grouped with the algae. They are different because they do or carry on photosynthesis and are plant parasites. In Ireland in the mid-1800's, about 1 million people died as a result of a famine caused by Phytophora (potato blight). Other species of this genus affect trees. 7. Charophyta (Stoneworts) are freshwater plants and generally grow anchored to the substratum by rhizoids with a shoot extending upward. The shoot then divides and forms nodes from which a whorl of side filaments projects. Charophyta reproductive structures develop at these nodes and are, along with the biflagellate sperm produced in the male gametangium, quite similar to those of mosses. These similarities have led some scientists to identify the charophytes as ancestors of the mosses. Their green color comes from chlorophylls a and b. 8. Chrysophyta (Golden algae)- are photosynthetic, unicellular organisms that are abundant in freshwater and marine environments. Chrysophytes contain chlorophylls a and c, which are masked by the accessory pigment fucoxanthin, a carotenoid. In many ways, golden algae are, biochemically and structurally similar to brown algae. Both golden algae and brown algae store food outside of the chloroplast in the form of polysaccharide laminarin, or chrysolaminarin. In both groups, motile cells have unequal flagella of similar structure. 6 Cyanobacteria (Blue-green algae)- Even though the Cyanobacteria are classified as bacteria (lacking a membrane-bounded nucleus) they are photosynthetic and are included among our algal collections. Cyanobacteria played a decisive role in elevating the level of free oxygen in the atmosphere of the early Earth. Cyanobacteria can change remarkably in appearance, depending on the environmental conditions. Blue-green algae are common in soil, in both salt and fresh water, and can grow over a wide range of temperatures. They have been found to form mats in Antarctic lakes under several meters of ice and are responsible for the beautiful colors of the hot springs at Yellowstone and elsewhere. Cyanobacteria can also occur as symbionts of protozoans, diatoms and lichen-forming fungi, and vascular plants. Some blue-greens can fix nitrogen as well as photosynthesize, allowing them to grow with only light, water, a few minerals, and the nitrogen and carbon dioxide in the atmosphere. Cyanobacteria are different in many important ways from other photosynthetic prokaryotes. Instead of the bacteriochlorophylls found in purple and green bacteria, blue-greens contain chlorophyll a, as in eucaryotic phototrophs, and, produce free oxygen as a byproduct of photosynthesis. Cyanobacteria, however, lack the organized chloroplasts of eukaryotes and have their photosynthetic apparatus distributed peripherally in the cytoplasm. The variety of striking colors exhibited by Cyanobacteria are a result of their major light- gathering pigments, the phycobilins, that

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