Q: A bacterial culture is in the log phase of growth. If the generation time is 30 minutes and you start with 1,000 cells, how many cells will there be after 2 hours?

$$N = 1,000 \times 2^4$ = 16,000$$

Question 1

Which of the following best describes a psychrotroph, and why are they significant in food microbiology?

Accepted Answer

They can grow at low temperatures (0–7°C) but have an optimum between 20–30°C, causing food spoilage in refrigerators.

Question 2

A bacterium is isolated from a salt lake with a NaCl concentration of 25%. Which term best describes its salt requirement?

Accepted Answer

Obligate halophile

Question 3

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

Accepted Answer

$$N = 2^n$$

Question 4

A culture medium contains peptone, beef extract, and agar. Which type of medium is this?

Accepted Answer

Complex medium

Question 5

Which of the following best explains why obligate anaerobes are killed by oxygen?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 6

A patient develops an infection on a catheter that is difficult to treat with antibiotics. Which microbial property is most likely responsible?

Accepted Answer

The bacteria are forming a biofilm.

Question 7

Which of the following best describes the function of buffers in bacterial growth media?

Accepted Answer

They maintain a stable pH by neutralizing acids produced during growth.

Question 8

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

Accepted Answer

Streak plate method

Question 9

Which of the following is a correct description of the stationary phase in a bacterial growth curve?

Accepted Answer

The rate of cell division equals the rate of cell death due to nutrient depletion and waste accumulation.

Question 10

A sample of water is filtered and the filter is placed on a nutrient agar plate. After incubation, 150 colonies are counted. If 100 mL of water was filtered, what is the bacterial concentration in the original sample?

Accepted Answer

$$1.5 	imes 10^3$ bacteria/mL

Question 11

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

Accepted Answer

It is not metabolized by most microbes and remains solid at incubation temperatures.

Question 12

Which of the following best describes the role of superoxide dismutase in aerobic bacteria?

Accepted Answer

It removes superoxide radicals by converting them to hydrogen peroxide and oxygen.

Question 13

A microbiologist is working with a highly infectious airborne pathogen. Which biosafety level (BSL) laboratory is required?

Accepted Answer

BSL-3

Question 14

Which of the following best describes a differential medium?

Accepted Answer

It contains substances that cause some bacteria to appear differently based on their metabolic properties.

Question 15

A bacterial culture is in the log phase of growth. If the generation time is 30 minutes and you start with 1,000 cells, how many cells will there be after 2 hours?

Accepted Answer

$$N = 1,000 	imes 2^4$ = 16,000$$

Question 16

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

Accepted Answer

Turbidity measurement

Question 17

Which of the following is a real-world example of the use of selective media?

Accepted Answer

Using bismuth sulfite agar to isolate Salmonella Typhi from a stool sample.

Question 18

Which of the following best explains why biofilms are a major concern in medical settings?

Accepted Answer

Biofilms are 1000 times more resistant to microbicides and are involved in 70% of infections.

Question 19

Which of the following best describes the function of phosphorus in microbial growth?

Accepted Answer

It is used in DNA, RNA, ATP, and phospholipids.

Question 20

A microbiologist is culturing a fastidious organism. Which type of medium is most appropriate?

Accepted Answer

Complex medium

Microbial Growth: Requirements, Culture, and Measurement

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