Chapter 27

Chapter 27 - Chapter 27 Bacteria and Archaea 5000 species...

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Chapter 27: Bacteria and Archaea 5000 species have been formally named and described—most by the morphological species concept It is certain in reality that tens of millions exist Over 400 species of bacteria are living in your gastrointestinal tract Another 500 species live in your mouth, of which just 300 have been described and named Most of these microbes (microscopic organisms) are bacteria or archaea, and virtually all are unnamed and undescribed The approximately 10 trillion cellsin you body are vastly outnumbered by the bacterial cells that live on and in you An estimated 10 12 bacterial cells live on your skin and an additional 10 14 cells occupy your stomach and intestines A mere teaspoon of good quality soil contains billions of microbial cells, most of which are bacteria and archaea A drop of seawater contains a population equivalent to that of a large city There is as much carbon in these cells as there is in all of the plants on Earth In terms of the total volume of living material on our planet, bacteria and archaea are dominant life forms In microbiology— the study of organisms that can be seen only with the aid of a microscope—this is an age of exploration and discovery 27.1 WHY DO BIOLOGISTS STUDY BACTERIA AND ARCHAEA? Bacteria and archaea form two of the three largest branches on the tree of life The third major branch or domain consists of eukaryotes and is called the Eukarya Virtually all members of the bacteria and archaea are unicellular and all are prokaryotic —meaning they lack a membrane bound nucleus These organisms are distinguished by several important features: species in the domain Bacteria have cell walls made primarily of peptidoglycan, plasma membranes similar to those found in eukaryotes, and ribosomes and RNA polymerase that are distinct in structure and function from the homologous structures in the Archaea and Eukarya Species in the domain Archaea have cell walls made of polysaccharides not found in bacterial or eukaryotic cell walls, unique plasma membranes, and ribosomes and RNA polymerase similar to those found in eukaryotes Prokaryotic cells are much small than eukaryotic cells and are simpler in overall form, or morphology Bacteria and Archaea are ancestral to eukaryotes and are much more diverse in the habitats they occupy and the molecules they can use as food These qualitites make them exceptionally interesting to study and important agents in medicine, industry, and quality of the environment Bacterial Diseases No archaea are known to cause disease in humans Bacteria that cause disease are said to be pathogenic
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Robert Koch was the first biologist to establish a link between a particular species of bacterium and a specific disease Koch hypothesized that bacteria might also be responsible for causing infectious diseases , which spread by being passed from an infected individual to an uninfected one
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This note was uploaded on 04/17/2008 for the course BIOL 202 taught by Professor Kopeny during the Spring '08 term at UVA.

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Chapter 27 - Chapter 27 Bacteria and Archaea 5000 species...

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