Question 1

Which of the following best explains why salt is used to preserve foods such as meats and pickles?

Accepted Answer

Salt increases osmotic pressure, causing plasmolysis in bacteria and inhibiting their growth.

Question 2

A bacterium that can grow in the presence or absence of oxygen, but produces more energy when oxygen is available, is classified as which of the following?

Accepted Answer

Facultative anaerobe

Question 3

A laboratory technician is culturing a bacterium that requires high concentrations of carbon dioxide and low oxygen. Which term best describes this organism?

Accepted Answer

Capnophile

Question 4

Which of the following statements about agar is correct?

Accepted Answer

Agar is a complex polysaccharide that solidifies culture media but is not metabolized by most bacteria.

Question 5

A water sample is suspected to contain a low concentration of coliform bacteria. Which direct method would be most appropriate to enumerate the bacteria?

Accepted Answer

Filtration followed by culturing on a nutrient pad

Question 6

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

Accepted Answer

Cells are dividing at a constant, exponential rate, and are most sensitive to adverse conditions.

Question 7

A microbiologist wants to isolate a pure culture from a mixed sample. Which method is most commonly used for this purpose?

Accepted Answer

Streak plate method

Question 8

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

Accepted Answer

Phosphorus

Question 9

A bacterial culture is transferred to a new medium and shows little to no increase in cell number for several hours, but metabolic activity is high. Which phase of growth is this?

Accepted Answer

Lag phase

Question 10

Which of the following equations correctly represents the calculation of the number of bacteria per milliliter in a plate count experiment?

Accepted Answer

$$N = C 	imes D$$

Question 11

A researcher is working with a bacterium that cannot survive in the presence of oxygen. Which of the following best explains why?

Accepted Answer

It lacks the enzymes to neutralize harmful forms of oxygen.

Question 12

Which of the following best describes the purpose of using phosphate salts in bacterial culture media?

Accepted Answer

To act as a buffer and maintain a stable pH.

Question 13

Which type of media would you use to both suppress the growth of unwanted bacteria and distinguish between different types of bacteria based on their appearance?

Accepted Answer

Selective and differential media

Question 14

A bacterial culture is in the stationary phase. Which of the following best explains what is happening in the culture?

Accepted Answer

The number of new cells formed is equal to the number of cells dying.

Question 15

Which of the following indirect methods of measuring microbial growth is most appropriate for estimating the number of bacteria in a highly turbid broth culture?

Accepted Answer

Turbidity measurement using a spectrophotometer

Question 16

A microbiologist is studying a fungus and wants to measure its growth. Which method is most appropriate?

Accepted Answer

Dry weight measurement

Question 17

Which of the following best describes the process of lyophilization for preserving microbial cultures?

Accepted Answer

Removing water by high vacuum and quickly freezing at $$-54^\circ C to$$ $$-72^\circ C$$

Question 18

A bacterial population doubles every 2 hours. If you start with 100 cells, how many cells will there be after 6 hours, assuming no cell death?

Accepted Answer

$$N = 100 	imes 2^3$ = 800$$

Question 19

Which of the following best explains why some pathogens, such as those causing leprosy and syphilis, cannot be grown on artificial media?

Accepted Answer

They require living host cells for growth.

Question 20

Which of the following is a plausible reason why the most probable number (MPN) method would be used instead of a plate count?

Accepted Answer

The bacteria being counted will not grow on solid media.

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

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