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rav65819_ch28_539-560 - 28 chapter Prokaryotes introduction...

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;;;;;;;; 28 chapter Prokaryotes introduction ONE OF THE HALLMARKS OF LIVING organisms is their cellular organization. You learned earlier that living things come in two basic cell types: ❐❒❏❋❁❒❙❏▼❅▲ and ❅◆❋❁❒❙❏▼❅▲✎
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To review, prokaryotes lack the membrane-bounded nucleus found in all eukaryotes, and they also have a much less complex cellular structure, lacking many of the organelles seen in eukaryotes (chapter 4). Prokaryotes are considerably smaller and more numerous than their eukaryotic counterparts. If we examined a human being closely, we would discover that there are approximately 10 prokaryotic cells living in or on the human body for every single human cell present—and there are trillions of human cells. Prokaryotic microbes play an important role in global ecology as well. Most biologists think prokaryotes were the first organisms to evolve. The diversity of eukaryotic organisms that currently live on Earth could not exist without prokaryotes because they make possible many of the essential functions of ecosystems. Prokaryotic photosynthesis, for example, is thought to have been the source for the oxygen in the ancient Earth’s atmosphere, and it still contributes significantly to oxygen production today. An understanding of prokaryotes is essential to understanding all life on Earth, past and present. concept outline 28.1 The First Cells Microfossils indicate that the first cells were probably prokaryotic Isotopic data indicate that carbon fixation is an ancient process Some hydrocarbons found in ancient rocks may have biological origins 28.2 Prokaryotic Diversity Prokaryotes are fundamentally different from eukaryotes Despite similarities, Bacteria and Archaea differ fundamentally Most prokaryotes have not been characterized 28.3 Prokaryotic Cell Structure Prokaryotes have three basic forms: Rods, cocci, and spiral Prokaryotes have a tough cell wall and other external structures The interior of prokaryotic cells is organized 28.4 Prokaryotic Genetics Conjugation depends on the presence of a conjugative plasmid Viruses transfer DNA by transduction
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Transformation is the uptake of DNA directly from the environment Antibiotic resistance can be transferred by resistance plasmids Variation can also occur by mutation 28.5 Prokaryotic Metabolism Prokaryotes acquire carbon and energy in four basic ways Some bacteria can infect other cells directly Bacteria are costly plant pathogens 28.6 Human Bacterial Disease Tuberculosis has infected humans for all of recorded history Bacterial biofilms are involved in tooth decay Bacteria can cause ulcers Many sexually transmitted diseases are bacterial Bacteria have been developed into bioweapons 28.7 Beneficial Prokaryotes Prokaryotes are involved in cycling important elements Prokaryotes may live in symbiotic associations with eukaryotes Bacteria are used in genetic engineering
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