Question 1

Which of the following best describes a facultative anaerobe?

Accepted Answer

An organism that can use oxygen for cellular respiration when it is present but can switch to fermentation in its absence.

Question 2

A microbiologist is culturing a bacterium that grows best at pH 5.5. Which term best describes this organism?

Accepted Answer

Acidophile

Question 3

Which enzyme is responsible for neutralizing superoxide radicals in aerobic bacteria?

Accepted Answer

Superoxide dismutase

Question 4

A bacterial culture is placed in a hypertonic solution. What is the most likely outcome for the cells?

Accepted Answer

Cells will lose water and undergo plasmolysis.

Question 5

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

Accepted Answer

They lack the enzymes needed to detoxify reactive oxygen species.

Question 6

A culture medium that contains only known quantities of all ingredients is called:

Accepted Answer

Defined medium

Question 7

Which of the following is a direct method for measuring microbial growth?

Accepted Answer

Serial dilution and viable plate count

Question 8

A bacterium isolated from a hot spring grows optimally at 75°C. Which category does it belong to?

Accepted Answer

Hyperthermophile

Question 9

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

Accepted Answer

It maintains a microbial culture in a continuous state of exponential growth by adding fresh medium and removing old culture.

Question 10

Which of the following statements about biofilms is TRUE?

Accepted Answer

Biofilms form as a result of quorum sensing and provide protection to the microorganisms within.

Question 11

A microbiologist wants to isolate a single species from a mixed culture. Which technique should they use?

Accepted Answer

Streak plate method

Question 12

Which of the following best describes the generation time of a bacterial species?

Accepted Answer

The time required for a bacterial population to double in number.

Question 13

Which of the following media would you use to select for Gram-negative bacteria and differentiate lactose fermenters?

Accepted Answer

MacConkey agar

Question 14

A scientist is studying a bacterium that can grow in the presence or absence of oxygen but does not use oxygen for metabolism. What is the best classification for this organism?

Accepted Answer

Aerotolerant anaerobe

Question 15

Which of the following equations correctly represents the conversion of oxygen to superoxide anion?

Accepted Answer

$$\mathrm{O_2$} + e^- \rightarrow \mathrm{O_2$}^{-}$$

Question 16

Which of the following is NOT a toxic form of oxygen?

Accepted Answer

Molecular oxygen ($$\mathrm{O_2$})$$

Question 17

A microbiologist is using the serial dilution and viable plate count method. If 0.1 mL of a $$10^{-5}$$ dilution yields 65 colonies, what is the original concentration of bacteria per mL?

Accepted Answer

$$6.5 	imes 10^8$ CFU/mL

Question 18

Which of the following best describes the lag phase of a bacterial growth curve?

Accepted Answer

Cells are adjusting to their environment and not dividing rapidly.

Question 19

Which preservation method would be most appropriate for storing a bacterial culture for decades?

Accepted Answer

Lyophilization

Question 20

Which of the following statements about nitrogen fixation is correct?

Accepted Answer

It is essential for converting atmospheric nitrogen into a form usable by living organisms.

Microbial Nutrition and Growth: Study Guide

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