Chapter 27 - Chapter 27 Diversification of the Eukaryotes...

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Chapter 27 Diversification of the Eukaryotes How Do Microbial Eukaryotes Affect the World Around Them? Many members of the Eukarya do not fit into the three familiar kingdoms of the Plantae, Animalia, and Fungi. Eukaryotes that are neither plants, animals, nor fungi are called protists or microbial eukaryotes (though not all are microbes) Protists are polyphyletic group ± not all taxa share a recent common ancestor ± some more closely related to animals (or fungi or plants) than to other protists ± More research needed to determine true phylogeny Great diversity of protist eukaryotes Most are microscopic, but some are large (e.g., giant kelp). Many are constituents of plankton — free floating, microscopic, aquatic organisms ± Plankton that are photosynthetic are called phytoplankton In marine food webs, phytoplankton are the primary producers Diatoms (a clade) are dominant phytoplankton – they are responsible for 1/5 of carbon fixation on Earth Primary producers are consumed by heterotrophs Endosymbiosis , where one organism lives inside another, is common in protists Dinoflagellates are common endosymbionts in animals and other microbial eukaryotes; Many radiolarians have photosynthetic endosymbiont – often, both organisms benefit from the relationship. Plasmodium is a p athogenic microbial eukaryote Causes malaria Part of its life cycle is spent as a parasite in red blood cells Female Anopheles mosquito is vector ; takes up gametes with blood, zygotes form in mosquito gut, and is passed to another human Trypanosomes ( kinetoplastids ) are some of the most deadly organisms on Earth causes sleeping sickness, leishmaniasis, and Chagas’ disease. Some chromalveolates , including diatoms, dinoflagellates, and haptophytes, can form “red tides” Color is from pigments in the dinoflagellates. Cell concentrations are extremely high Some produce neurotoxins that kill fish – Gonyaulax produces a toxin that accumulates in shellfish Diatoms store oil as an energy reserve Over millions of years, diatoms died and sank to the ocean floor, and through
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chemical and physical changes form petroleum and natural gas deposits Foraminiferans secrete shells of calcium carbonate Discarded shells make up extensive deposits of limestone -- some beach sands made of fragments of “foram” shells How Did the Eukaryotic Cell Arise? Main events in evolution of eukaryotic cells: origin of a flexible cell surface origin of a cytoskeleton origin of a nuclear envelope appearance of digestive vesicles (vacuoles) endosymbiotic acquisition of certain organelles First step may have been loss of cell wall by ancestral prokaryote, increasing flexibility allowed membrane infolding ± à ± can sustain larger cell volume and more rapid metabolism ± infolded plasma membrane attached to a chromosome in an ancestral
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Chapter 27 - Chapter 27 Diversification of the Eukaryotes...

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