Question 1

Which of the following best describes the optimum growth temperature for thermophiles?

Accepted Answer

Between 50°C and 60°C

Question 2

A microbiologist is attempting to culture a bacterium that requires many specific vitamins and amino acids. Which type of medium should be used?

Accepted Answer

Chemically defined medium

Question 3

Which equation correctly represents the total number of cells after $$n$$ generations, starting from a single cell?

Accepted Answer

$$N = 2^n$$

Question 4

A bacterium is found growing only at the bottom of a tube of thioglycolate broth. Which term best describes its oxygen requirements?

Accepted Answer

Obligate anaerobe

Question 5

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms are rarely involved in human infections.

Question 6

Which of the following best explains why food in a deep container cools more slowly than food in a shallow container in a refrigerator?

Accepted Answer

The surface area to volume ratio is lower in deep containers, slowing heat loss.

Question 7

Which of the following is a correct description of a facultative halophile?

Accepted Answer

Can tolerate high salt concentrations but does not require them

Question 8

A culture medium contains the following: peptone, beef extract, sodium chloride, agar, and water. Which type of medium is this?

Accepted Answer

Complex medium

Question 9

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

Accepted Answer

Stationary phase

Question 10

A sample is diluted in a series of 1:10 dilutions, and 54 colonies are counted on a plate from the $$10^{-3}$$ dilution. What is the original concentration of bacteria in the sample?

Accepted Answer

$$5.4 	imes 10^5$ CFU/mL

Question 11

Which of the following best describes the function of reducing media?

Accepted Answer

To remove oxygen and support the growth of obligate anaerobes

Question 12

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

Accepted Answer

Turbidity measurement with a spectrophotometer

Question 13

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

Accepted Answer

It liquefies at 100°C and solidifies at about 40°C

Question 14

A bacterium that grows best at pH 5.5 is most likely a:

Accepted Answer

Acidophile

Question 15

Which of the following statements about the Most Probable Number (MPN) method is TRUE?

Accepted Answer

It is based on statistical estimation from positive growth in dilution tubes

Question 16

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

Accepted Answer

They are usually enzyme cofactors required in small amounts

Question 17

A microbiologist wants to isolate a pure culture from a mixed sample. Which method should be used?

Accepted Answer

Streak plate method

Question 18

Which of the following best describes the log phase of bacterial growth?

Accepted Answer

Cells are dividing at the fastest possible rate

Question 19

Which of the following is a characteristic of selective media?

Accepted Answer

It suppresses the growth of unwanted microbes

Question 20

A bacterium is described as a chemoheterotroph. Which of the following statements is TRUE about its nutritional requirements?

Accepted Answer

It uses organic molecules for both energy and carbon

Microbial Growth: Physical and Chemical Requirements, Culture Methods, and Measurement

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