Q: A sample initially contains $$N_0 = 20$ bacterial cells. If the generation time is 30 minutes, how many cells will there be after 3 hours, assuming exponential growth? Use N_t$$ = $$N_0$$ \times 2^n$$.

$$N_t = 20 \times 2^6$ = 1,280$$ cells

Question 1

Which of the following best describes the process of binary fission in prokaryotes?

Accepted Answer

A single cell divides into two identical daughter cells after replicating its DNA.

Question 2

A sample initially contains $$N_0 = 20$ bacterial cells. If the generation time is 30 minutes, how many cells will there be after 3 hours, assuming exponential growth? Use N_t$$ = $$N_0$$ 	imes 2^n$$.

Accepted Answer

$$N_t = 20 	imes 2^6$ = 1,280$$ cells

Question 3

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms are always harmful and have no beneficial uses.

Question 4

Which environmental factor is most likely to limit the growth of a mesophile in a hot spring (70°C)?

Accepted Answer

Temperature

Question 5

A bacterium that grows best at pH 9.0 is classified as a(n):

Accepted Answer

Alkaliphile

Question 6

Which of the following best explains why obligate anaerobes cannot survive in the presence of oxygen?

Accepted Answer

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

Question 7

Which type of culture medium would you use to isolate Neisseria species from a clinical specimen?

Accepted Answer

Thayer-Martin agar

Question 8

A microbiologist wants to count only the viable cells in a sample. Which method should they use?

Accepted Answer

Plate count method

Question 9

Which of the following best describes a facultative anaerobe?

Accepted Answer

Grows best in the presence of oxygen but can also grow without it.

Question 10

Which of the following is a chemically defined medium?

Accepted Answer

Glucose-salts agar

Question 11

A food company wants to preserve food by limiting microbial growth. Which strategy is most effective based on water availability?

Accepted Answer

Increasing the concentration of salt or sugar to lower water availability

Question 12

Which group of microorganisms would you expect to find in the Dead Sea, where salt concentrations are extremely high?

Accepted Answer

Extreme halophiles

Question 13

Which of the following best describes the function of a chemostat in microbial culture?

Accepted Answer

It maintains a continuous culture by adding nutrients and removing wastes.

Question 14

Which of the following is a primary metabolite produced during the exponential phase of bacterial growth?

Accepted Answer

Amino acids

Question 15

A scientist is studying a bacterium that can grow in the presence or absence of oxygen but does not use oxygen for energy production. What is the most likely classification?

Accepted Answer

Aerotolerant anaerobe

Question 16

Which of the following best explains why refrigeration slows food spoilage?

Accepted Answer

It slows the growth of mesophilic bacteria by lowering the temperature below their optimum range.

Question 17

Which of the following is a selective and differential medium used to isolate Gram-negative intestinal bacteria?

Accepted Answer

MacConkey agar

Question 18

A bacterium that uses sunlight for energy and CO$$_2 as a $$carbon source is classified as a:

Accepted Answer

Photoautotroph

Question 19

Which of the following best describes the role of nitrogen fixation in microbial growth?

Accepted Answer

It converts atmospheric N$$_2$$ into ammonia, which can be incorporated into organic molecules.

Question 20

Which method would be most appropriate for estimating the number of bacteria in a water sample with very low cell density?

Accepted Answer

Membrane filtration

Microbial Growth: Principles, Environmental Factors, and Laboratory Measurement CH4

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