13. Given a log phase bacterial culture with 1 x 10 cells per ml and a generatio
ID: 198590 • Letter: 1
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13. Given a log phase bacterial culture with 1 x 10 cells per ml and a generation time of 30 minutes, how long does it take the culture to reach a density of 6.4 x 10 cells per ml? A. 1 hour B. 2 hours C. 3 hours D. 4 hours E. 6 hours 14. Which of the following is NOT a possible reason for entry into the stationary phase of growth? A. Nutrient limitation B. Limited oxygen availability C. Toxic waste accumulation D. Critical population density reached E. All of the above are possible reasons 15. are associated with certain chronic infections and do not respond to antibiotic treatment. A. Bacteria B. Daughter cells C. Pathogens D. Persisters E. None of the above means bacteria cannot grow under lab conditions but may grow 16 under appropriate conditions. A. Death phase B. Genetically programed cell death C. Starvation response D. Viable but nonculturable E. None of the above 17. A culture in a closed vessel to which no additional medium is added and from which no waste products are removed is called a(n) culture. A. Batch B. Continuous C. Enrichment D. Fed-batch E. Semi-continuous 18. Which of the following is NOT true of chemostats? A. An open system B. An essential nutrient is in limiting quantities C. Has a photocell that measures the turbidity D. Maintains cells in log phase E. All of the above are trueExplanation / Answer
16.D. viable but nonculturable. These organisms are viable but since their growth conditions like media and other physical factors are not known, they cannot be cultured.
17. A. Batch. In continuous culture media is continuosly added and cells removed. In fed-batch also media is added but cells are not removed.
18. E. All of the above are true for chemostats
19. C. Spectrophotometry. All other techniques give the direct count. Spectrophotometry does not give the number of cells. It only checks the absorbance based on whih the number of cells can be roughly estimated.
20. A. True. Plating the culture after diluting it gives countable number of colony forming units which when multiplied with dilution factor gives the actual number of cells.
22. D.Spectrophotometry. Since cells are turbid, lesser light will pass through the cuvette as the cell density increases and vice versa.
23. B.False. Most microbes are planktonic
24. C. Susceptible to UV light and antibiotics. When biofilms are formed the celss become less susceptible to UV light and antibiotics.
25.C. Only prokaryotes use quorum sensing to coordinate certain behaviours. Almost all organisms be it prokaryotes or eukaryotes have cell to cell communication.
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