Question 1

Which of the following best describes a mesophile?

Accepted Answer

A microorganism that grows optimally at temperatures between 20°C and 45°C.

Question 2

A bacterium that can tolerate salt concentrations up to 15% but does not require high salt to grow is classified as a:

Accepted Answer

Facultative halophile

Question 3

Which enzyme is responsible for breaking down hydrogen peroxide into water and oxygen in bacteria?

Accepted Answer

Catalase

Question 4

Why are obligate anaerobes unable to survive in the presence of oxygen?

Accepted Answer

They lack enzymes to neutralize reactive oxygen species.

Question 5

Which of the following best describes the function of quorum sensing in bacteria?

Accepted Answer

It allows bacteria to coordinate gene expression based on population density.

Question 6

A culture medium that contains only known quantities of pure chemicals is called:

Accepted Answer

Defined (synthetic) medium

Question 7

Which type of medium would you use to distinguish between bacteria that can ferment lactose and those that cannot?

Accepted Answer

Differential medium

Question 8

What is the main advantage of using a streak plate method in microbiology?

Accepted Answer

It allows for the isolation of single colonies to obtain pure cultures.

Question 9

Which phase of the bacterial growth curve is characterized by rapid cell division and exponential increase in cell number?

Accepted Answer

Log (exponential) phase

Question 10

A sample is expected to have very few bacteria. Which enumeration method is most appropriate?

Accepted Answer

Filtration followed by plating

Question 11

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

Accepted Answer

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

Question 12

Which of the following best explains why biofilm-associated bacteria are often more resistant to antibiotics than free-swimming bacteria?

Accepted Answer

Biofilms provide a protective matrix that limits antibiotic penetration and slows bacterial metabolism.

Question 13

A bacterium that grows best at pH 2 is classified as a(n):

Accepted Answer

Acidophile

Question 14

Which of the following is a correct statement about the pour plate method?

Accepted Answer

It is often used to estimate the number of bacteria in food samples.

Question 15

If a bacterial culture starts with 100 cells and doubles every 30 minutes, how many cells will there be after 2 hours? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 100 	imes 2^4$ = 1600$$

Question 16

Which of the following best describes a facultative anaerobe?

Accepted Answer

It can grow in the presence or absence of oxygen.

Question 17

Which of the following is a real-world consequence of Clostridium perfringens being an obligate anaerobe and endospore former?

Accepted Answer

It can survive cooking processes and cause foodborne illness in anaerobic foods like casseroles.

Question 18

Which of the following best describes the stationary phase of the bacterial growth curve?

Accepted Answer

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

Question 19

Which method would provide a quick, rough estimate of bacterial cell density in a liquid culture?

Accepted Answer

Measuring turbidity with a spectrophotometer

Question 20

Which of the following best explains why microaerophiles grow only in low oxygen concentrations?

Accepted Answer

They have limited ability to detoxify reactive oxygen species.

Microbial Growth: Environmental Factors, Culturing, and Enumeration

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