Question 1

Which of the following best describes a strict anaerobe, and how could you experimentally determine if a microbe is a strict anaerobe?

Accepted Answer

It grows only at the bottom of a thioglycollate broth tube; test by incubating in the absence of oxygen.

Question 2

If bacterial cells are grown in media containing radioactive phosphorus ($$^{32}P$$), in which cellular macromolecule would you expect to find the highest concentration of $$^{32}P$$?

Accepted Answer

Nucleic acids

Question 3

Why is sugar added to fruit to make jams and jellies, in terms of microbial growth?

Accepted Answer

Sugar creates a hypertonic environment, causing plasmolysis and inhibiting microbial growth.

Question 4

Which of the following best describes a biofilm?

Accepted Answer

A complex community of microorganisms attached to a surface and embedded in a self-produced matrix.

Question 5

What is the main problem with psychrotrophs in relation to food safety?

Accepted Answer

They spoil food by growing at low temperatures, such as those in refrigerators.

Question 6

Which biosafety level (BSL) is appropriate for teaching laboratories working with organisms that pose minimal potential hazard to laboratory personnel and the environment?

Accepted Answer

BSL-1

Question 7

A pastry chef accidentally inoculated a cream pie with 6 S. aureus cells. If the generation time is 60 minutes, how many cells would be present after 7 hours? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 6 	imes 2^7$ = 768$$

Question 8

Why do bacteria not grow if nitrogen and phosphorus are not added to beaches after an oil spill?

Accepted Answer

Nitrogen and phosphorus are required for the synthesis of proteins and nucleic acids, which are essential for bacterial growth.

Question 9

Which enzyme is responsible for breaking down hydrogen peroxide into water and oxygen, and why is this important for aerobic organisms?

Accepted Answer

Catalase; it prevents accumulation of toxic hydrogen peroxide.

Question 10

Which of the following best explains why refrigeration and freezing preserve foods?

Accepted Answer

Low temperatures slow down or stop microbial metabolism and growth.

Question 11

A prokaryotic cell from another planet is a psychrophile, an obligate halophile, and an obligate aerobe. What can you infer about the planet's environment?

Accepted Answer

It is cold, salty, and has abundant oxygen.

Question 12

Which of the following best describes the function of superoxide dismutase in bacteria?

Accepted Answer

It converts superoxide radicals to hydrogen peroxide and oxygen.

Question 13

Why must you measure the light transmission of both a culture tube and a medium-only tube when using a spectrophotometer to estimate bacterial growth?

Accepted Answer

To account for the absorbance of the medium itself, ensuring only bacterial growth is measured.

Question 14

Which of the following is an advantage of the plate count method over the spectrophotometer method for measuring bacterial growth?

Accepted Answer

Plate count measures only living cells capable of forming colonies.

Question 15

Which of the following best explains why Clostridium is killed by oxygen, while Streptococcus (also catalase-negative) is not?

Accepted Answer

Clostridium lacks superoxide dismutase and cannot detoxify reactive oxygen species.

Question 16

In an experiment, yeast cells are grown in glucose–minimal salts broth at 30°C with and without aeration. Which culture will produce more ATP, and why?

Accepted Answer

The aerobic culture, because aerobic respiration yields more ATP per glucose molecule.

Question 17

An organism that has peroxidase and superoxide dismutase but lacks catalase is most likely a(n):

Accepted Answer

Aerotolerant anaerobe

Question 18

Which of the following best describes the role of biofilms in pathogenesis?

Accepted Answer

Biofilms protect bacteria from the host immune system and increase resistance to antibiotics.

Question 19

If you were to track radioactive nitrogen ($$^{15}N) in a $$bacterial cell, in which macromolecule would you expect to find the highest concentration?

Accepted Answer

Proteins

Microbial Growth and Control: Chapter 6 Microbiology Study Guide

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