Question 1

Which of the following best describes the 'danger zone' for rapid bacterial growth in food, as shown in the temperature diagram?

Accepted Answer

Between 20°C and 50°C

Question 2

A bacterium that grows only at the bottom of a thioglycollate broth tube is most likely a(n):

Accepted Answer

Obligate anaerobe

Question 3

Which enzyme catalyzes the following reaction? $$2\ H_2O_2 \xrightarrow{catalase} 2\ H_2O + O_2$

Accepted Answer

Catalase

Question 4

A culture medium that contains yeast extract, peptone, and glucose is best described as:

Accepted Answer

Complex

Question 5

Which of the following best explains why agar is used as a solidifying agent in microbiological media?

Accepted Answer

It is not generally metabolized by microbes and has a suitable melting/solidifying range

Question 6

Which of the following statements about psychrotrophs is correct?

Accepted Answer

They are commonly responsible for food spoilage in refrigerators

Question 7

A microbiologist wants to isolate a bacterium that can degrade phenol from a soil sample containing thousands of other bacteria. Which type of medium should she use?

Accepted Answer

Enrichment medium

Question 8

Which of the following best describes the function of buffers in bacterial growth media?

Accepted Answer

They neutralize acids produced by bacteria to maintain pH

Question 9

A bacterial culture is growing in a medium with 10% NaCl. Which term best describes this organism?

Accepted Answer

Obligate halophile

Question 10

Which of the following equations represents the reaction catalyzed by superoxide dismutase?

Accepted Answer

$$O_2^- + 2$$\ H^+ \xrightarrow{superoxide\ dismutase} H_2O_2 + $$O_2$$

Question 11

A microbiologist is using the streak plate method to isolate colonies. What is the main purpose of this technique?

Accepted Answer

To obtain pure cultures by separating individual cells

Question 12

Which of the following best describes the growth pattern of a facultative anaerobe in thioglycollate broth?

Accepted Answer

Growth throughout the tube, but denser at the top

Question 13

A bacterial sample is diluted 1:10,000 and 1 mL is plated. After incubation, 32 colonies are counted. What is the concentration of bacteria in the original sample?

Accepted Answer

$$3.2 	imes 10^5$ CFU/mL

Question 14

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

Accepted Answer

Turbidity

Question 15

Which of the following best explains why hyperthermophiles are found in hot springs associated with volcanic activity?

Accepted Answer

They use sulfur in their metabolic activity and thrive at high temperatures

Question 16

Which of the following statements about binary fission is correct?

Accepted Answer

It results in two genetically identical daughter cells

Question 17

Which of the following is a chemical requirement for microbial growth that makes up more than 50% of the dry weight of a bacterial cell?

Accepted Answer

Carbon

Question 18

A microbiologist is using a spectrophotometer to measure bacterial growth. What is being measured in this method?

Accepted Answer

The amount of light scattered by a bacterial suspension (turbidity)

Question 19

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

Accepted Answer

They usually function as enzyme cofactors

Question 20

Which of the following best explains why molds and yeasts can grow at lower pH than most bacteria?

Accepted Answer

They possess enzymes that function optimally at acidic pH

Microbial Growth: Requirements, Culture Methods, and Measurement

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