Q: A batch culture of E. coli is inoculated with $$N_0 = 100$ cells. If the generation time is 20 minutes, how many cells will there be after 2 hours of exponential growth? Use N_n$$ = $$N_0$$ \times 2^n$$.

$$N_n = 100 \times 2$$^{12}$$ = 409,600$$

Question 1

Which of the following best describes the function of the FtsZ ring during bacterial cell division?

Accepted Answer

It defines the division plane and recruits enzymes for septum formation.

Question 2

A batch culture of E. coli is inoculated with $$N_0 = 100$ cells. If the generation time is 20 minutes, how many cells will there be after 2 hours of exponential growth? Use N_n$$ = $$N_0$$ 	imes 2^n$$.

Accepted Answer

$$N_n = 100 	imes 2$$^{12}$$ = 409,600$$

Question 3

Which adaptation is most likely found in a psychrophilic bacterium living in Antarctic sea ice?

Accepted Answer

Increased glycine and more $$\alpha-$$helices in proteins

Question 4

During which phase of the batch culture growth curve is the rate of cell division equal to the rate of cell death?

Accepted Answer

Stationary phase

Question 5

A chemostat is set up with a limiting nutrient. What happens if the dilution rate exceeds the specific growth rate of the microorganism?

Accepted Answer

The culture is washed out and cell density drops to zero.

Question 6

Which of the following best explains why obligate anaerobes are killed by exposure to oxygen?

Accepted Answer

They lack superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 7

Which of the following is a correct mathematical expression for the generation time $$g in $$terms of total time $$t$$ and number of generations $$n$$?

Accepted Answer

$$g = \frac{t}{n}$$

Question 8

Which of the following is NOT a typical adaptation of thermophilic microorganisms?

Accepted Answer

Increased content of unsaturated fatty acids in membranes

Question 9

A bacterium is isolated from Mono Lake, a highly alkaline environment. Which adaptation is it most likely to possess?

Accepted Answer

Na+/H+ antiporter to maintain pH homeostasis

Question 10

Which of the following best describes the role of bactoprenol in peptidoglycan synthesis?

Accepted Answer

It acts as a lipid carrier to transport peptidoglycan precursors across the membrane.

Question 11

A facultative anaerobe is grown in a test tube with an oxygen gradient. Where will it grow best and why?

Accepted Answer

At the surface, because it can use oxygen for faster growth but can also grow anaerobically.

Question 12

Which of the following best describes the difference between disinfection and sterilization?

Accepted Answer

Disinfection reduces microbial load, while sterilization destroys all vegetative cells, endospores, and viruses.

Question 13

Which of the following environmental parameters is most likely to limit the growth of a halotolerant bacterium in a high-sugar environment?

Accepted Answer

Osmolarity (water activity)

Question 14

A culture of Bacillus subtilis is in stationary phase. Which of the following is most likely occurring?

Accepted Answer

Secondary metabolites such as antibiotics are being produced.

Question 15

Which of the following is a correct description of the minimum temperature for microbial growth?

Accepted Answer

The lowest temperature at which growth and metabolism can proceed.

Question 16

Which of the following best explains why exponential growth cannot continue indefinitely in a batch culture?

Accepted Answer

Nutrient depletion and waste accumulation eventually limit growth.

Question 17

Which of the following is a key adaptation of barophilic (piezophilic) bacteria to high hydrostatic pressure?

Accepted Answer

Short and unsaturated fatty acid chains in membranes

Question 18

A culture of Staphylococcus aureus is exposed to UV radiation. Which of the following is the most likely molecular effect?

Accepted Answer

Formation of pyrimidine dimers in DNA

Question 19

Which of the following best describes the function of autolysins during peptidoglycan synthesis?

Accepted Answer

They hydrolyze glycosidic bonds to allow insertion of new peptidoglycan.

Prokaryotic Cell Cycle and Microbial Growth: Structured Study Notes

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