CHAPTER 25

CHAPTER 25 - CHAPTER 25 PROTISTS Protists o Unicellular,...

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CHAPTER 25 PROTISTS Protists o Unicellular, colonial, or simple multicellular organisms that have a eukaryotic cell organization o First eukaryotes to evolve INTRODUCTION TO THE PROTISTS Unicellular o Most protists o Each cell forming a complete organism capable of performing all the functions characteristic of life Colonies o Loosely connected groups of cells Coenocytic o Multinucleate mass of cytoplasm Multicellular o Composed of many cells o Relatively simple body forms without specialized tissues Mutualism o More or less equal partnership where both partners benefit Commensalism o One partner benefits and the other is unaffected Parasitism o One partner lives on or in another and metabolically depends on it Plankton o Floating, often microscopic organisms that inhabit surface waters and are the base of the food web in aquatic ecosystems EVOLUTION OF THE EUKARYOTES Zooflagellates o First eukaryotes o Heterotrophic unicellular protists that have flagella Mitochondria and chloroplasts probably originated from endosymbionts Serial endosymbiosis o Hypothesis that certain eukaryotic organelles, particularly mitochondria and chloroplasts, arose from symbiotic relationships between larger cells and smaller prokaryotes that were incorporated and lived within them A consensus is emerging in eukaryote classification Ultrastructure
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o Fine details of cell structure revealed by electron microscopy Monophyletic o Evolved from a common ancestor Paraphyletic o Contains some, but not all, of the descendants of a common eukaryote ancestor REPRESENTATIVE PROTISTS Excavates are anaerobic zooflagellates Zooflagellates o Mostly heterotrophic, unicellular organisms with spherical or elongated bodies Flagella o Long, whip-like organelles used for movement Excavates o Endosymbionts and live in anoxic environments o Lack mitochondria Diplomonads o Retain some characteristics thought to have been present in ancient protists o One or two nuclei, no functional mitochondria, no Golgi complex, and up to 8 flagella Trichonymphs o Specialized excavates with hundreds of flagella that live in the guts of termites and wood-eating cockroaches Discicristates include euglenoids and trypanosomes
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CHAPTER 25 - CHAPTER 25 PROTISTS Protists o Unicellular,...

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