Q: A bacterial culture is started with 1 cell. If the generation time is 30 minutes, how many cells will there be after 3 hours, assuming no cell death? Use the formula $$N = N_0$ \times 2^n$$, where $$N_0 is $$the initial number of cells and $$n is $$the number of generations.

$$N = 1 \times 2^6$ = 64$$ cells

Question 1

Which of the following best describes the process of binary fission in bacteria?

Accepted Answer

The chromosome is replicated, the cell elongates, and then constricts at the center, resulting in two genetically identical daughter cells.

Question 2

A bacterial culture is started with 1 cell. If the generation time is 30 minutes, how many cells will there be after 3 hours, assuming no cell death? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N_0 is $$the initial number of cells and $$n is $$the number of generations.

Accepted Answer

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

Question 3

Which phase of the bacterial growth curve is characterized by a plateau in the number of living cells due to a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 4

In a chemostat, which of the following is true regarding the maintenance of bacterial cultures?

Accepted Answer

Nutrients are continuously added and waste is removed, maintaining cells in logarithmic growth.

Question 5

Which method would be most appropriate for estimating the number of viable bacteria in a very dilute water sample?

Accepted Answer

Most probable number (MPN) method

Question 6

A facultative anaerobe is best described as an organism that:

Accepted Answer

Utilizes oxygen when present but can also grow in its absence.

Question 7

Which enzyme is responsible for converting hydrogen peroxide ($$H_2O_2) $$into water and oxygen, protecting cells from oxidative damage?

Accepted Answer

Catalase

Question 8

A patient with diabetic foot ulcers develops gas gangrene. Which of the following best explains why Clostridium perfringens thrives in this environment?

Accepted Answer

Dead tissue in the ulcers creates an anaerobic microenvironment ideal for obligate anaerobes.

Question 9

Which of the following best describes the growth of Listeria monocytogenes in refrigerated foods?

Accepted Answer

It is capable of growth at temperatures between 0°C and 50°C, allowing it to grow in refrigerated foods.

Question 10

Which type of media would you use to isolate a fastidious organism that cannot synthesize certain nutrients?

Accepted Answer

Enriched media

Question 11

A microbiologist wants to distinguish between lactose-fermenting and non-lactose-fermenting bacteria. Which type of medium should be used?

Accepted Answer

Differential medium, such as MacConkey agar

Question 12

Which of the following statements about biosafety levels (BSL) is correct?

Accepted Answer

BSL-4 requires the highest level of containment and is used for exotic, life-threatening agents.

Question 13

Which of the following methods is most effective for sterilizing heat-sensitive medical instruments?

Accepted Answer

Glutaraldehyde in 2% solution (Cidex)

Question 14

Which of the following statements about pasteurization is true?

Accepted Answer

It kills non-spore-forming pathogens and reduces spoilage microbes, but does not sterilize.

Question 15

Which of the following is a limitation of using UV radiation for microbial control?

Accepted Answer

It has little penetrating power and must be directly exposed to the surface.

Question 16

A hospital uses copper door handles to reduce microbial contamination. What is the mechanism by which copper acts as an antimicrobial agent?

Accepted Answer

It binds to proteins, inhibiting enzymatic activity.

Question 17

Which of the following best explains why high concentrations of salt or sugar can be used to preserve foods?

Accepted Answer

They create a hypertonic environment, causing plasmolysis and inhibiting microbial growth.

Question 18

Which of the following statements about the disk-diffusion method is correct?

Accepted Answer

It determines the effectiveness of chemical agents by measuring the zone of inhibition around each disk.

Question 19

Which of the following best describes the action of alcohols as disinfectants?

Accepted Answer

They rapidly denature proteins and disrupt membranes, leading to cell lysis.

Question 20

A laboratory technician is using a HEPA filter in a biosafety cabinet. What is the primary function of the HEPA filter?

Accepted Answer

To physically remove microbes, endospores, and viruses from the air.

Microbial Growth and Control: Dynamics, Measurement, and Environmental Factors

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