Q: Which of the following equations correctly represents the calculation of colony-forming units (CFU) from a plate count?

$$\mathrm{CFU} = \text{number of colonies} \times \text{dilution factor}$$

Question 1

Which of the following best describes a mesophile?

Accepted Answer

A microorganism that grows best at moderate temperatures, such as 37°C.

Question 2

A bacterial culture is incubated at 80°C and shows optimal growth. Which category does this organism most likely belong to?

Accepted Answer

Hyperthermophile

Question 3

Which of the following equations correctly represents the calculation of colony-forming units (CFU) from a plate count?

Accepted Answer

$$\mathrm{CFU} = 	ext{number of colonies} 	imes 	ext{dilution factor}$$

Question 4

Which physical method is most effective for complete sterilization, including destruction of spores and viruses?

Accepted Answer

Autoclaving at 121.5°C and 15 psi for 20 minutes

Question 5

A bacterium is placed in a hypertonic solution. What is the most likely outcome?

Accepted Answer

Water will move out of the cell, causing plasmolysis.

Question 6

Which type of microorganism would most likely thrive in a soda lake with a pH of 10?

Accepted Answer

Alkaliphile

Question 7

Which of the following statements about obligate anaerobes is correct?

Accepted Answer

They are killed by the presence of oxygen.

Question 8

Which enzyme is responsible for neutralizing superoxide radicals in aerobic bacteria?

Accepted Answer

Superoxide dismutase

Question 9

A hospital uses UV lamps in its operating rooms. What is the primary purpose of this method?

Accepted Answer

To reduce the number of airborne microbes

Question 10

Which of the following is true regarding antiseptics?

Accepted Answer

They can be safely applied to living tissues.

Question 11

A culture medium contains 5% NaCl. Which type of microorganism is most likely to grow best in this environment?

Accepted Answer

Halophile

Question 12

Which phase of bacterial growth is characterized by equal rates of cell division and cell death?

Accepted Answer

Stationary phase

Question 13

If a bacterial culture has a generation time of 30 minutes, how many cells will result from a single cell after 3 hours of exponential growth? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 1 	imes 2^6$ = 64$$

Question 14

Which of the following is a correct definition of sterilization?

Accepted Answer

The complete destruction of all microorganisms, including spores and viruses.

Question 15

Which factor does NOT directly affect the efficacy of a chemical disinfectant?

Accepted Answer

Color of the disinfectant

Question 16

Which of the following is an example of a bacteriostatic agent?

Accepted Answer

A chemical that prevents bacterial growth without killing them

Question 17

A scientist wants to estimate the number of bacteria in a liquid culture using turbidity. Which instrument should they use?

Accepted Answer

Spectrophotometer

Question 18

Which of the following best describes the effect of desiccation on microorganisms?

Accepted Answer

It slows metabolic activities, but many microbes remain viable.

Question 19

Which of the following is a correct statement about haloduric organisms?

Accepted Answer

They do not prefer salty environments but can survive there.

Question 20

Which of the following is the lowest temperature at which all organisms in a pure culture are killed within a specified time?

Accepted Answer

Thermal death point (TDP)

Microbial Growth: Factors, Laboratory Cultivation, and Inhibition

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