Question 1

Which of the following best describes binary fission in bacteria?

Accepted Answer

A process where one mother cell divides into two genetically identical daughter cells.

Question 2

A bacterial culture starts with 1 cell. After 10 generations, how many cells will there be, assuming no cell death? Use the formula $$N = 2^n$$, where $$N is $$the number of cells and $$n is $$the number of generations.

Accepted Answer

$$N = 2$$^{10}$$ = 1,024$$

Question 3

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 4

A bacterium that grows optimally at 37°C and is commonly found in the human body is classified as a:

Accepted Answer

Mesophile

Question 5

Which of the following equations correctly represents the action of superoxide dismutase in detoxifying superoxide radicals?

Accepted Answer

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

Question 6

Which type of bacteria would you expect to find growing at the bottom of a tube of solid growth medium, where oxygen concentration is lowest?

Accepted Answer

Obligate anaerobes

Question 7

A bacterium isolated from a hot spring that grows optimally at 90°C is most likely a:

Accepted Answer

Hyperthermophile

Question 8

Which of the following is a chemical requirement for microbial growth that is a component of ATP, DNA, and RNA?

Accepted Answer

Phosphorus

Question 9

Why are biofilms clinically significant in medical settings?

Accepted Answer

They are up to 1,000 times more resistant to microbicides and are involved in 70% of infections.

Question 10

Which of the following best describes a selective medium?

Accepted Answer

A medium that suppresses unwanted microbes and encourages the growth of desired microbes.

Question 11

A microbiologist wants to culture an obligate anaerobe. Which of the following methods would be most appropriate?

Accepted Answer

Using a reducing medium containing sodium thioglycolate and an anaerobic jar.

Question 12

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

Accepted Answer

Turbidity measurement with a spectrophotometer

Question 13

A culture medium that contains beef extract and peptone, but not all components are chemically known, is classified as:

Accepted Answer

Complex medium

Question 14

Which of the following best explains why a colony does not grow to fill the entire Petri plate?

Accepted Answer

Nutrients become depleted and waste products accumulate, limiting further growth.

Question 15

Which of the following is a reason why psychrotrophs are significant in food microbiology?

Accepted Answer

They can grow at refrigerator temperatures and cause food spoilage.

Question 16

Which of the following is a trace element required by some bacteria as an enzyme cofactor?

Accepted Answer

Zinc

Question 17

A microbiologist is using the streak plate method. What is the primary purpose of this technique?

Accepted Answer

To isolate pure cultures from a mixture of bacteria.

Question 18

Which of the following best describes the function of catalase in bacteria?

Accepted Answer

It converts hydrogen peroxide into water and oxygen: $$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 19

Which of the following is a correct statement about the use of enrichment media?

Accepted Answer

It increases the number of a desired microbe to detectable levels.

Question 20

A bacterial suspension is counted using a Petroff-Hausser cell counter. If 14 cells are counted in a square with a volume of $$1/1,250,000 ml$$, what is the concentration of cells per ml?

Accepted Answer

$$14 	imes 1,250,000 = 17,500,000$$ cells/ml

Microbial Growth: Requirements, Measurement, and Culture Techniques

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