Содержание
- 2. Binary fission Unlike eukaryotic cells, prokaryotic cells do not have a cell cycle with a specific
- 3. Budding, in yeast and a few bacteria, is the development of a small, new cell from
- 4. Fig. 6-3 Phases of Growth depend on the genetics of the particular bacteria and on the
- 5. As the number of microbes increases, nutrients decrease, wastes build up, oxygen becomes depleted, the population
- 6. Fig. 6-4 Scientists can induce synchronous growth - all bacteria in the population divide at the
- 7. Fig. 6-6 .. Measuring Bacterial Growth = number of live(viable) organisms per milliliter Serial dilution Dilute
- 8. Fig. 6-7 and standard plate counts Transfer a known volume onto a solid plate (agar). Spread
- 9. Count The colonies under a magnifying lens and multiply the number of colonies on the plate
- 10. Fig. 6-9 Direct Microscopic Counts – Petroff-Hausser counting chamber A known volume of bacterial suspension is
- 11. Fig. 6-10 Most Probable Number Used when samples contain too few organisms, as in food and
- 12. Filtration is another method of estimating the size of a small bacterial population. A known volume
- 13. Factors Affecting Bacterial Growth: Physical factors like pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure,
- 14. Temperature: Psychrophiles do best at 15-20°C but some can do well at 0°C. (Seawater remains liquid
- 15. The temperature range of an organisms is determined largely by its enzymes. The optimum temperature is
- 16. Fig. 6-15 Oxygen: Aerobes require oxygen to grow and anaerobes do not. Obligate aerobes must have
- 17. Obligate anaerobes are killed by the highly reactive and toxic for of oxygen superoxide, which is
- 18. Moisture: All actively metabolizing cell require a water environment. Only spores can exist in a dormant
- 19. Osmotic pressure: Environments that contain dissolved substances exert osmotic pressure. The pressure outside of a cell
- 20. Most bacterial cells can tolerate a wide range of solute concentrations in their environment because they
- 21. Radiation: such as gamma rays and ultraviolet light cause mutations (changes in DNA) and even kill
- 22. Nutritional Factors Carbon sources – Photoautotrophic organisms reduce carbon dioxide to glucose etc. Both autotrophic and
- 23. Nutritional complexity, the number of nutrients an organism must have to survive, is determined by the
- 24. Location of Enzymes Endoenzymes, the usual, inside the cell Exoenzymes are released through the cell membrane
- 25. Adaptation to limited nutrients Some synthesize increased amounts of enzymes to obtain and use a larger
- 26. Fig. 6-17 Sporulation, the formation of endospores, occurs in Bacillus, Clostridium, etc. See Figure 6.18 Bacteria
- 27. A pure culture of a single species is needed to study it’s characteristics and a medium
- 28. Culturing bacteria in the lab requires knowledge of their nutritional needs. Some organisms still cannot be
- 29. Media used to isolate and identify particular microorganisms, from patients with infectious diseases, are selective, differential,
- 30. Fig. 6-20 Controlling Oxygen content of media is important. Obligate aerobes may need oxygen gas bubbled
- 31. Maintaining cultures Maintained indefinitely in a pure culture called a stock culture By making subcultures in
- 32. Fig. 6-23 Multiple diagnostic tests allow simultaneous determination of an organism’s reaction to a variety of
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