Question 1

Which of the following best describes a psychrotroph?

Accepted Answer

An organism that grows optimally at 15°C and is responsible for most food spoilage at refrigeration temperatures.

Question 2

A food product is left at 30°C for 6 hours. Which group of bacteria is most likely to cause spoilage under these conditions?

Accepted Answer

Mesophiles

Question 3

Which of the following equations correctly represents the exponential growth of bacteria, where $$N is $$the final number of cells, $$N_0 is $$the initial number of cells, and $$n is $$the number of generations?

Accepted Answer

$$N = N_0$ 	imes 2^n$$

Question 4

A bacterium has a generation time of 30 minutes. If you start with 100 cells, how many cells will there be after 3 hours of growth under ideal conditions?

Accepted Answer

6,400

Question 5

Which phase of the bacterial growth curve is characterized by metabolic activity without an increase in cell number?

Accepted Answer

Lag phase

Question 6

Why are most pathogens classified as mesophiles?

Accepted Answer

Their optimum growth temperature is close to human body temperature ($$\sim 37^\circC).$$

Question 7

Which of the following best explains why salted meats are less likely to spoil?

Accepted Answer

High osmotic pressure causes plasmolysis in bacteria, inhibiting their growth.

Question 8

Which enzyme is required by aerobic bacteria to neutralize superoxide radicals ($$O_2$$^-$$)?

Accepted Answer

Superoxide dismutase (SOD)

Question 9

A microbiologist wants to isolate a bacterium that can grow in the absence of oxygen but is killed by its presence. Which type of medium should be used?

Accepted Answer

Reducing medium

Question 10

Which of the following statements about differential media is correct?

Accepted Answer

It allows the differentiation of colonies of desired microbes from others based on observable changes.

Question 11

A culture medium that contains beef extract, peptone, and agar is best described as:

Accepted Answer

Complex medium

Question 12

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

Accepted Answer

The rate of cell death equals the rate of new cell formation.

Question 13

Which of the following is a trace element required for enzyme cofactors in microbial growth?

Accepted Answer

Zinc (Zn)

Question 14

A bacterium is found growing at pH 3. Which term best describes this organism?

Accepted Answer

Acidophile

Question 15

Which of the following best explains why food should be refrigerated promptly after cooking?

Accepted Answer

To prevent the food from remaining in the 'danger zone' (20–50$$^\circC) $$where rapid bacterial growth and toxin production can occur.

Question 16

Which of the following is NOT a chemical requirement for microbial growth?

Accepted Answer

Light

Question 17

A facultative anaerobe is best described as an organism that:

Accepted Answer

Can grow with or without oxygen, but grows better with oxygen.

Question 18

Which of the following best describes the process of plasmolysis in bacteria?

Accepted Answer

The plasma membrane shrinks away from the cell wall due to water loss in a hypertonic solution.

Question 19

Which of the following is a correct sequence of events in binary fission?

Accepted Answer

DNA replicates, cell wall and membrane begin to divide, cross wall forms, cells separate.

Question 20

Which of the following best explains why the log phase is the most sensitive to antibiotics?

Accepted Answer

Cells are metabolically active and rapidly dividing, making them more susceptible to agents that target cell wall synthesis or metabolism.

Chapter 6: Microbial Growth: Physical and Chemical Requirements, Media, and Growth Dynamics

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