Algae David Fan I.
Algae A. Characteristics 1. Algae are all photosynthetic (autotrophy) organisms that aren’t plants or animals 2. Plant-like protists 3. Unicellular or multicellular, eukaryotic, motile or nonmotile 4. Unlike plants, algae lack roots, leaves and flowers 5. Major types: chrysophytes, diatoms, dinoflagellates, red algae, brown algae, and green algae. B. Classification 1. Divided into seven main divisions for convenience, not evolutional or biological significance: Chrysophyta, Pyrrophyta, Euglenophyta, Chlorophyta, Rhodophyta, Phaeophyta, and Xanthophyta. 2. Classification is based on the combination of photosynthetic pigments contained in the plastids, the cellular structure and organization, composition of the cell wall, the presence or absence of flagella, reproductive means, and motility C. Chysophyta (Golden Algae) 1. Diatoms 2. Contain the photosynthetic pigments chlorophyll c and carotenoids such as fucoxanthin that give them a yellowish brown color in addition to the chlorophyll a that is common to all algae. 3. Unicellular; motile. Some are non-motile 4. Cell walls contain silicon compounds, pectin and cellulose 5. In absence of light or food, chrysophytes can become falculatively heterotrophic; they feed on diatoms and bacteria 6. Closely related to diatoms 7. Store food reserves as oil droplets giving buoyancy to position closely to sun to store energy 8. Usually reproduce asexually, sexually only when needed D. Pyrrophyta (Fire Algae) 1. Dinoflagellates 1. Unicellular 2. Chlorophyll C 3. Photosynthetic 4. Closely resemble ciliated protists 5. Perpendicularly arranged flagella, one at the posterior end and another located within a groove and that spins as the cell swims. 6. Like diatoms, they store energy as oil droplets, also starch
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7. Some are motile; free swimming. Some are non-motile; live in symbiotic relationships a. Many coral have dinoflagellates living in them 8. Tend to form algal blooms 9. Salt and freshwater 10. Reproduce asexually Euglenophyta 1. Third strictly unicellular division of algae 2. Chlorophylls A, B and carotenoids 3. Live in freshwater 4. Flagella 5. Light sensitive eyespot that searches for environment conducive to photosynthesis 6. Multiple chloroplasts 7. Store food as starch F. Chlorophyta (Green Algae) 1. Most diverse and well known group of algae 2. Like all plants, they have Chlorophyll A, B and carotenoids 3. Mostly unicellular, freshwater 4. Some are multicellular, saltwater 5. Some live in terrestrial environments 6. Filamentous algae forms green mat that coats top of lakes Rhydophyta (Red Algae) 1. Marine 2. Mostly multicellular 3. Contain phycobilins, photosynthetic pigments that capture green and blue light that penetrates deep into the water. Helps them survive at deep depths 4. Some have cell walls made of calcium carbonate; help build coral reefs 5. Reproduce asexually and sexually (meiosis) Phaeophyta (Brown Algae) 1. Chlorophylls A and C and fucoxanthin 2. Have structures similar to plants 3. Mostly live in saltwater, 4 species live in freshwater 4. Attach to rocks near water or float near surface of water 5. Gas-filled floats keep blades closer to sunlight 6. Mostly multicelllar 7. Brown and red algae together constitute seaweed Xanthophyta (Yellow-Green Algae) 1. Primarily inhabit freshwater 2. No chlorophyll B or fucoxanthin 3. Have Chlorophyll C 4. Mostly unicellular, and have flagella 5. Some are colonial (live in group, not motile
I. Reproduction 1. Some reproduce asexually by mitosis 2. Others reproduce by fragmentation or spore formation 1. Flagellated spores are common to aquatic algae 2. Nonmotile spores are common to terrestrial algae 3. Some reproduce sexally by meosis J. Ecological Importance 1. As primary producers, algae play a vital niche in many ecosystems 2. They play a vital part in aquatic food webs, produce most of he world’s oxygen and provide iodine and protein for humans 3. However, when algae are given too many favorable conditions, they can over reproduce and cause algae blooms K. Economic Importance 1. Many East Asian cultures eat red and green algae (seaweed) 2. Carrageen is used to improve texture in products 3. Other extracts are used in products