Question 1

Which of the following best describes a chemoautotroph?

Accepted Answer

An organism that uses carbon dioxide as its carbon source and inorganic chemicals as its energy source.

Question 2

A bacterial culture starts with 200 cells. If the cells divide every 40 minutes, how many cells will there be after 4 hours? Use the formula $$N = N_0$ 	imes 2^n.$$

Accepted Answer

25,600

Question 3

Which of the following best explains why most organisms cannot use atmospheric nitrogen ($$N_2) $$directly for growth?

Accepted Answer

Most organisms lack the enzymes to break the strong triple bond in $$N_2.$$

Question 4

A microbiologist wants to isolate salt-tolerant bacteria and distinguish those that ferment mannitol. Which type of medium should she use?

Accepted Answer

A selective and differential medium

Question 5

Which group of microbes would most likely be responsible for food spoilage in a refrigerator?

Accepted Answer

Psychrotrophs

Question 6

A patient develops a persistent infection on a catheter despite antibiotic treatment. Which property of biofilms most likely contributes to this persistence?

Accepted Answer

Biofilms provide a protective matrix and slow growth, making cells less susceptible to antibiotics.

Question 7

Which of the following best describes the difference between selective and differential media?

Accepted Answer

Selective media inhibit some microbes; differential media display visible biochemical differences among those that grow.

Question 8

A bacterium is classified as a facultative anaerobe. Where would you expect to see the most growth in a thioglycollate broth tube?

Accepted Answer

Heaviest at the top, but growth throughout the tube

Question 9

Which of the following is a trace element required by cells, often as an enzyme cofactor?

Accepted Answer

Iron

Question 10

A culture begins with 80 cells and undergoes 4 generations. How many cells are present at the end? Use $$N = N_0$ 	imes 2^n.$$

Accepted Answer

Question 11

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death, with the population size remaining relatively constant?

Accepted Answer

Stationary phase

Question 12

A microbiologist uses a spectrophotometer to measure the turbidity of a bacterial culture. Which of the following is true about this method?

Accepted Answer

It is an indirect method that measures both living and dead cells.

Question 13

Which of the following best explains why refrigeration preserves food but does not sterilize it?

Accepted Answer

Refrigeration slows enzyme activity and membrane transport, delaying growth but not killing all microbes.

Question 14

A bacterial cell is placed in a hypertonic solution. What is the most likely outcome?

Accepted Answer

The cell will lose water, and the cytoplasm will shrink (plasmolysis).

Question 15

Which of the following best describes quorum sensing in bacteria?

Accepted Answer

A chemical communication system that coordinates gene expression based on population density.

Question 16

A microbiologist wants to maintain a bacterial culture in the log phase for an extended period. Which device should she use?

Accepted Answer

A chemostat

Question 17

Which of the following is the correct formula for calculating the number of generations ($$n) if $$the total time and generation time are known?

Accepted Answer

$$n = \frac{	ext{total time}}{	ext{generation time}}$$

Question 18

Which of the following best explains why a viable plate count reports colony-forming units (CFU) instead of cells?

Accepted Answer

A colony may arise from a single cell or a cluster of cells, so CFU reflects this uncertainty.

Question 19

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

Accepted Answer

Turbidity measurement

Question 20

A bacterium grows best at pH 9.5. How would you classify this organism?

Accepted Answer

Alkalinophile

Microbial Nutrition and Growth: Study Guide and Key Concepts

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