Question 1

Which of the following best describes the effect of a hypertonic environment on a bacterial cell?

Accepted Answer

The cell will undergo plasmolysis as water leaves the cell.

Question 2

A bacterium isolated from a hot spring that grows optimally at $$70^\circ C is $$most likely classified as a:

Accepted Answer

Thermophile

Question 3

Which of the following is a primary use of phosphorus in microbial cells?

Accepted Answer

Component of DNA, RNA, and ATP

Question 4

Which equation correctly represents the action of superoxide dismutase (SOD) in detoxifying superoxide radicals?

Accepted Answer

$$2O_2^- + 2H^+ \rightarrow O_2$ + H_2O_2$$

Question 5

A microbiologist wants to culture an obligate anaerobe. Which method would be most appropriate?

Accepted Answer

Use of reducing media containing sodium thioglycolate

Question 6

Which of the following best describes a selective medium?

Accepted Answer

A medium that contains inhibitors to suppress unwanted microbes and encourage desired microbes

Question 7

A bacterial culture is in the stationary phase of growth. Which of the following best explains what is occurring?

Accepted Answer

The rate of cell division equals the rate of cell death.

Question 8

Which biosafety level (BSL) requires the use of a sealed, negative pressure laboratory and workers wearing 'space suits' with an air supply?

Accepted Answer

BSL-4

Question 9

A sample contains $$10^6$$ bacteria. If the generation time is 30 minutes, how many bacteria will be present after 2 hours of exponential growth?

Accepted Answer

$$1.6 	imes 10^8$

Question 10

Which of the following is NOT a direct method for measuring microbial growth?

Accepted Answer

Turbidity measurement with a spectrophotometer

Question 11

Which type of microorganism would most likely be isolated from a jar of pickles preserved in vinegar (pH 3)?

Accepted Answer

Acidophile

Question 12

Which of the following statements about agar is FALSE?

Accepted Answer

It is used as a nutrient source for most bacteria.

Question 13

Which of the following best describes the function of trace elements in microbial growth?

Accepted Answer

They are used as enzyme cofactors.

Question 14

A facultative anaerobe is best described as an organism that:

Accepted Answer

Can grow with or without oxygen, using fermentation or anaerobic respiration when oxygen is absent.

Question 15

Which of the following is a correct description of the streak plate method?

Accepted Answer

It is used to isolate pure cultures from a mixed population.

Question 16

Which of the following is a reason why buffers are added to growth media?

Accepted Answer

To minimize pH changes caused by microbial metabolism.

Question 17

Which of the following best explains why food preserved with high concentrations of salt or sugar resists spoilage?

Accepted Answer

High solute concentration causes plasmolysis in microbes, inhibiting their growth.

Question 18

Which of the following is a characteristic of complex media?

Accepted Answer

It contains extracts and digests of yeasts, meat, or plants.

Question 19

Which of the following is the best method to preserve a bacterial culture for decades?

Accepted Answer

Lyophilization (freeze-drying)

Question 20

A microbiologist wants to estimate the number of bacteria in a water sample. Which method would be most appropriate if the expected bacterial count is very low?

Accepted Answer

Filtration followed by plating on nutrient agar

Microbial Growth: Requirements, Culture, and Measurement

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