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Unformatted text preview: 1 Chapter 16 Chapter 16 Microbial Life: Prokaryotes and Protists 2 3 PROKARYOTES 4 16.1 Prokaryotes are diverse and widespread Prokaryotic cells are smaller than eukaryotic cells. Prokaryotes range from 15 m in diameter. Eukaryotes range from 10100 m in diameter. The collective biomass of prokaryotes is at least 10 times that of all eukaryotes. 5 16.1 Prokaryotes are diverse and widespread Prokaryotes live in habitats too cold, too hot, too salty, too acidic, and too alkaline for eukaryotes to survive. Some bacteria are pathogens, causing disease. But most bacteria on our bodies are benign or beneficial. 6 16.1 Prokaryotes are diverse and widespread Several hundred species of bacteria live in and on our bodies, decomposing dead skin cells, supplying essential vitamins, and guarding against pathogenic organisms. Prokaryotes in soil decompose dead organisms, sustaining chemical cycles. 7 16.2 External features contribute to the success of prokaryotes Prokaryotic cells have three common cell shapes. Cocci are spherical prokaryotic cells. They sometimes occur in chains that are called streptococci. Bacilli are rod-shaped prokaryotes. Bacilli may also be threadlike, or filamentous. Spiral prokaryotes are like a corkscrew. Short and rigid prokaryotes are called spirilla . Longer, more flexible cells are called spirochetes . 8 9 16.2 External features contribute to the success of prokaryotes Nearly all prokaryotes have a cell wall. Cell walls provide physical protection and prevent the cell from bursting in a hypotonic environment. When stained with Gram stain , cell walls of bacteria are either Gram-positive, with simpler cell walls containing peptidoglycan , or Gram-negative, with less peptidoglycan, and more complex and more likely to cause disease. 10 11 16.2 External features contribute to the success of prokaryotes The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharides or protein. The capsule enables prokaryotes to adhere to their substrate or to other individuals in a colony and shields pathogenic prokaryotes from attacks by a hosts immune system. 12 13 16.2 External features contribute to the success of prokaryotes Some prokaryotes have external structures that extend beyond the cell wall. Flagella help prokaryotes move in their environment. Hairlike projections called fimbriae enable prokaryotes to stick to their substrate or each other. 14 15 16.3 Populations of prokaryotes can adapt rapidly to changes in the environment Prokaryote population growth occurs by binary fission, can rapidly produce a new generation within hours, and can generate a great deal of genetic variation by spontaneous mutations, increasing the likelihood that some members of the population will survive changes in the environment....
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This document was uploaded on 10/30/2011 for the course BIOL 1402 at Texas Tech.
- Fall '08