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rav65819_ch29_561-580

rav65819_ch29_561-580 - 29 FOR MORE THAN HALF OF the long...

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;;;;;;;; 29 FOR MORE THAN HALF OF the long history of life on Earth, all life was microscopic. The biggest organisms that existed for over 2 billion years were single-celled bacteria fewer than 6 m m thick. These prokaryotes lacked internal membranes, except for invaginations of surface membranes in photosynthetic bacteria. The first evidence of a different kind of organism is found in tiny fossils in rock 1.5 billion years old. These fossil cells are much larger than bacteria (up to 10 times larger) and contain internal membranes and what appear to be small, membrane-bounded structures. The complexity and diversity of form among these single cells is astonishing. The step from relatively simple to quite complex cells marks one of the most important events in the evolution of life, the appearance of a new kind of organism, the eukaryote. Eukaryotes that are clearly not animals, plants, or fungi have been lumped together and called protists.
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chapter Protists introduction 500 m μ concept outline 29.1 Defining Protists Protista is not monophyletic Monophyletic clades have been identified among the protists 29.2 Eukaryotic Origins and Endosymbiosis Fossil evidence dates the origins of eukaryotes The nucleus and ER arose from membrane infoldings Mitochondria evolved from engulfed aerobic bacteria Chloroplasts evolved from engulfed photosynthetic bacteria Endosymbiosis was not a rare occurrence Genes have migrated from endosymbiotic organelles Mitosis evolved in eukaryotes 29.3 General Biology of the Protists Protist cell surfaces vary widely Protists have several means of locomotion Protists have a range of nutritional strategies Protists reproduce asexually and sexually Protists are the bridge to multicellularity 29.4 Diplomonads and Parabasalids: Flagellated Protists Lacking Mitochondria Diplomonads have two nuclei Parabasalids have undulating membranes
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29.5 Euglenozoa: A Diverse Group in Which Some Members Have Chloroplasts Euglenoids are free-living eukaryotes with anterior flagella Kinetoplastids are parasitic 29.6 Alveolata: Protists With Submembrane Vesicles Dinoflagellates are photosynthesizers with distinctive features Apicomplexans include the malaria parasite Ciliates are characterized by their mode of locomotion 29.7 Stramenopila: Protists With Fine Hairs Brown algae include large seaweeds Diatoms are unicellular organisms with double shells Oomycetes, the “water molds,” have some pathogenic members 29.8 Rhodophyta: Red Algae 29.9 Choanoflagellida: Possible Animal Ancestors 29.10 Protists Without a Clade Amoebas are paraphyletic Foraminifera fossils created huge limestone deposits Slime molds exhibit “group behavior” 561 rav65819_ch29_561-580.indd 561 rav65819_ch29_561-580.indd 561 12/7/06 9:41:23 AM 12/7/06 9:41:23 AM 29.1 Defining Protists Protists are the most diverse of the four kingdoms in the domain Eukarya. Compartmentalization is the key feature that distinguishes protists and other eukaryotes from archaea and bacteria.
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