Cells Are Most Sensitive To Penicillin During Which Phase Of The Growth Curve

5. Explain why O2-containing atmospheres kill some bacteria.

6. Explain why photoautotrophs are the primary producers.

7. Distinguish between a selective medium and a differential medium.

8. Explain what occurs during each of the five phases of growth.

9. Explain how the environment of a colony differs from that of a liquid broth.

10. Describe a detrimental and a beneficial effect of biofilms.

Multiple Choice

1. E. coli is present in a liquid sample at a concentration of between 104 and 106 bacteria per ml. To determine the precise number of living bacteria in the sample, it would be best to...

A. use a counting chamber.

B. plate out an appropriate dilution of the sample on nutrient agar.

C. determine cell number by using a spectrophotometer.

D. Any of these three methods would be satisfactory.

E. None of these three methods would be satisfactory.

2. E. coli, a facultative anaerobe, is grown on the same solid medium, but under two different conditions: one aerobic, the other anaerobic. The size of the colonies that grow would be.

A. the same under both conditions.

B. larger when grown under aerobic conditions.

C. larger when grown under anaerobic conditions.

3. A soil sample is placed in liquid and the number of bacteria in the sample determined in two ways: (1) by colony count and (2) by counting the cells in a counting chamber (slide). How would the results compare?

A. Methods 1 and 2 would give approximately the same number of bacteria.

B. Many more bacteria would be estimated by method 1.

C. Many more bacteria would be estimated by method 2.

D. Depending on the soil sample, sometimes method 1 would be higher and sometimes method 2 would be higher.

4. Nutrient broth is an example of a.

A. synthetic medium.

B. complex medium.

C. selective medium.

D. indicator medium.

E. defined medium.

5. E. coli does not require vitamin E in the medium in which it grows. This is because E. coli...

A. does not require vitamin E for growth.

B. gets vitamin E from its host.

C. can substitute another vitamin for vitamin E in its metabolism.

D. can synthesize vitamin E from the simple compounds provided in the medium.

E. is a chemoheterotroph.

6. Cells are most sensitive to penicillin during which phase of the growth curve?

A. lag B. log C. stationary

D. death E. more than one of these.

7. Streptomyces cells would most likely synthesize antibiotics during which phase of the growth curve?

A. lag B. log C. stationary

D. death E. more than one of these.

8. In general, bacteria in nature, compared with their growth in the laboratory,.

A. grow more slowly.

B. grow faster.

C. usually grow at the same rate.

9. If there are 103 cells per ml at the middle of log phase, and the generation time of the cells is 30 minutes, how many cells will there be 2 hours later?

Review Questions

10. The major effect of a temperature of 60°C on a mesophile is to.

A. destroy the cell wall.

B. denature proteins.

C. destroy nucleic acids.

D. destroy the cytoplasmic membrane.

E. cause the formation of endospores.

Applications

1. You are a microbiologist working for a pharmaceutical company and discover a new metabolite that can serve as a human medication. Your company asked you to oversee the production of the metabolite. What are some of the factors you must consider if you need to grow 5,000-liter cultures of the bacteria?

2. High-performance boat manufacturers know that bacteria can collect on a boat, ruining the boat's hydrodynamic properties. Periodic cleaning of the boat's surface and repainting eventually ruin that surface and do not solve the problem. A boat-manufacturing facility recently hired you to help with this problem because of your microbiology background. What strategies can you use to come up with a long-term remedy for the problem?

Critical Thinking Questions

1. This figure shows a growth curve plotted on a non-logarithmic, or linear, scale. Compare this with figure 4.17. In both figures, the number of cells increases dramatically during the log or exponential phase. In this phase, the cell number increases more and more rapidly (this effect is more apparent in the accompanying figure). Why should the increase be speeding up?

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