Protista 2011 - Role of protists in the biosphere...

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Unformatted text preview: Role of protists in the biosphere Autotrophic protists produce over 75% of our atmospheric oxygen Decomposer protists play an important role in eating dead organic matter and recycling materials in our ecosystem Certain kinds cause red tide and lead to build up of toxins in shellfish (can poison man; kill aquatic life) When certain inorganic nutrients are high, can cause bloom of protists; they multiply and cover top of water so no light penetrates and aquatic plants and animals die leading to eutrophication The Origin of the Eukaryotic Cell The modern eukaryotic cell arose from an ancestral prokaryote. Probable steps included loss of the cell wall inward folding of the plasma membrane. Figure 27.2 The Origin of the Eukaryotic Cell An infolded plasma membrane attached to the chromosome may have led to formation of a nuclear envelope. A primitive cytoskeleton evolved. figure 27-03a.jpg The Origin of the Eukaryotic Cell Prokaryotic cells incorporated as endosymbionts gave rise to eukaryotic organelles. Peroxisomes may have been the first organelles of endosymbiotic origin. Mitochondria evolved from proteobacteria, Chloroplasts from cyanobacteria. Cells with nuclei probably appeared before those with mitochondria. A History of Endosymbiosis Primary endosymbiosis of a cyanobacterium and a eukaryote gave rise to the chloroplasts of photosynthetic protists Figure 27.29 A History of Endosymbiosis Secondary endosymbiosis of eukaryotes with unicellular green or red algae gave rise to the chloroplasts of euglenoids, stramenopiles, and other groups. A cell of one of those groups, in tertiary endosymbiosis, gave rise to another type of chloroplast. Cyanobacterium Heterotrophic eukaryote Primary endosymbiosis Red algae Green algae Secondary endosymbiosis Secondary endosymbiosis Plastid Dinoflagellates Apicomplexans Ciliates Stramenopiles Euglenids Chlorarachniophytes Plastid Alveolates extremely diverse assortment of eukaryotes no longer classified in a single kingdom Many textbooks do not consider Protista to be a kingdom Most protists are unicellular some are colonial or multicellular the most nutritionally diverse of all eukaryotes Photoautotrophs: contain chloroplasts Heterotrophs: absorb organic molecules or ingest larger food particles Mixotrophs: combine photosynthesis and heterotrophic nutrition Protists General Biology of the Protists Most are aquatic some live within other organisms. The great majority are unicellular and microscopic many are multicellular and a few are enormous. General Biology of the Protists Protozoan is an outdated term applied to protists once classified as animals. Alga is an outdated term applied to photosynthetic protists. General Biology of the Protists...
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Protista 2011 - Role of protists in the biosphere...

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