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Bacteria and Archaea

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20.1 Prokaryotes Are a Biological Success Story

1. Prokaryotes are important in many ways. They contribute gases to the atmosphere, form the bases of food webs, and fix nitrogen. More than a billion years ago, they gave rise to certain organelles.  
2. Prokaryotes are very abundant and diverse and occupy a great variety of habitats.  
3. Many prokaryotes are studied in the laboratory on plates of agar supplemented with appropriate nutrients, but others remain poorly studied because they cannot be cultured.  

20.2 Parts of a Prokaryotic Cell

4. Like other organisms, prokaryotic cells contain DNA and ribosomes and are bounded by a cell membrane. Essential Study Partner

Art Activity
Nonphotosynthetic Bacterium

Art Activity
5. DNA along with some RNA and protiens associate in an area called the nucleoid. Plasmids are circles of DNA in addition to the chromosome.  
6. Some bacteria wait out harsh conditions protected in endospores.  
7. A cell wall surrounds most prokaryotic cells. Gram staining reveals differences in cell wall architecture to group bacteria.  
8. Pili are projections that allow cells to adhere to surfaces or other cells. Flagella provide movement.  
9. A glycocalyx outside the cell wall provides adherence or protection from host immune system cells.  

20.3 How Microbiologists Distinguish and Describe Prokaryotes

10. Traditionally, microbiologists have classified prokaryotes based on cell morphology, metabolic capacities, physiological tests, or habitat. Essential Study Partner
11. Bacteria are spherical cocci, spiral-shaped spirilla, or variations of these. Archaea may have other shapes.  
12. Prokayotes can be classified based on how they acquire carbon and energy. Autotrophs acquire carbon from inorganic sources, and heterotrophs obtain carbon from other organisms. A phototroph derives energy from the sun, and a chemotroph by oxidizing organic or inorganic chemicals.  
13. Obligate aerobes require oxygen, facultative anaerobes can live whether or not ogygen is present, and obligate anaerobes cannot function cannot function in the presence of oxygen.  
14. Microbiologists are currently using molecular data, including signature sequences that are unique to certain groups of organisms, to reconsider traditional taxonomic classification of prokaryotes.  

20.4 Prokaryotes Transfer Genes Vertically and Horizontally

15. Binary fission is division of a prokaryotic cell to yield two daughter cells. It is vertical gene transfer because DNA goes from one generation to the next.  
16. In transformation, cells take up pieces of naked DNA from the environment. In transduction, a virus transfers DNA from one cell to another. In conjugation, a sex pilus transfers DNA from one cell to another. These are routes of horizontal gene transfer.  

20.5 How Prokaryotes Affect Humans

17. Koch's postulates are used to demostrate whether a type of micro-organism causes a particular set of symptoms.  
18. Pathogenic bacteria are transmitted in air, by direct contact, via arthropod vectors, or in food and water.  
19. Bioweapons are formulated from highly virulent bacteria, viruses, or fungi. A bioweapon attack would be difficult to detect, trace, and treat.  
20. Prokaryotes are used in the manufacture of many foods, drugs, and other chemicals. They are also used for treating sewage and cleaning the environment.  

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