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BIOL 120
Simon Cheung

Lecture 3 Autotroph - an organism that can make its own food through photosynthesis; self feeder Heterotroph - an organism that obtains food from other organisms; other feeder Mixotroph - an organism that has bothe autotrophic and heterotrophic abilities Algae  Challenge: harvesting light energy  Endosymbiosis played a key role in the evolution of algae  Euglena:  Most live in fresh water  Have two flagella  Have a pyrenoid - protein rich structure containing Rubisco  Eye spot and light detector to avoid bright light  Some species are mixotrophs  Reproduce asexually  Carbohydrate is stored as glucose polymer "paramylon granules"  Phylum Chromophyta (yellow-green algae):  Most live in fresh water  Most unicellular but some multicellular - colonial, filamentous, coenocytic  Most have two flagella  Chloroplasts move in response to changes in light intensity - avoiding light damage  Reproduction predominantly asexual - fragmentation or spores  Haptophytes:  Majority in oceans - tropics  About 50% of photosynthesis in mid-Atlantic  2 disc-shaped chloroplasts  Two flagella and a haptonema  Clump in gelatinous colonies  Phaseocystis produces UV absorbing compounds and release dimethylsulfide Lecture 3  Multicellular:  Brown algae (kelp) - sessiles, heteromorphic generations, good habitats for other animals, source of algin (paint, cosmetics)  Red algae (seaweeds) - comples life cycles, use for production of nori, agar, and carrageenan  Green algae - share common ancestor with plants • Phylum Chlorophyta (green algae): o Mostly freshwater o Some terrestrial o Have chloroplasts a and b o Store starch inside plastids  Class Charophyceae:  Unicellular, colonial, and multicellular  Coleochaetales and charales are the closest relatives of plants among all algae  Charales form mineralized cell walls - stonewarts  Have morphological features in common with vascular plants - apical growth, develop phragmoplasts and cell plates during mitosis, have a ligning like compound, reproductive cells protected Challenges:  Giving up the sea of moderation: getting out of the water  Staying wet when things get dry The environment was changing:  Approximately 2% oxygen in atmosphere 450-700 million years ago - ozone filters out UV light  Fossil records of land plants first occur around 450 mya (liverwort fragments) - possible to live on land  Less UV but water is essential and required for growth and reproduction  Constrained to moist environment  Size constraints imposing on gravity BRYOPHYTES (MOSS):  Gametophyte - consists of haploid cells (one of two multicellular forms of a plant) Lecture 3  Sporop
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