Q: A bacterial population starts with 100 cells and has a generation time of 30 minutes. How many cells will there be after 3 hours of exponential growth? Use the formula $$N = N_0$ \times 2^n$$, where $$n is $$the number of generations.

$$N = 100 \times 2^6$ = 6400$$ cells

Question 1

Which of the following best describes the growth pattern of mesophilic bacteria?

Accepted Answer

They grow optimally at temperatures between $$25^{\circ}C$ and 40$$^{\circ}$$C.$$

Question 2

A microbiologist wants to isolate bacteria that can degrade phenol from a soil sample containing thousands of other bacteria. Which culture technique should be used?

Accepted Answer

Enrichment culture

Question 3

Which enzyme catalyzes the reaction $$2O_2^- + 2H^+ \rightarrow O_2$ + H_2O_2 to $$detoxify superoxide radicals in bacteria?

Accepted Answer

Superoxide dismutase (SOD)

Question 4

A bacterial culture is growing in a medium with a pH of 4. Which group of bacteria is most likely to thrive in this environment?

Accepted Answer

Acidophiles

Question 5

Which of the following best explains why food in a large, deep container cools more slowly in a refrigerator than food in a shallow container?

Accepted Answer

The center of the deep container remains in the 'danger zone' temperature range longer, allowing bacteria like Bacillus cereus to multiply.

Question 6

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms are easily destroyed by standard microbicides.

Question 7

A bacterium is found to grow only at the bottom of a test tube of solid growth medium. Which term best describes its oxygen requirements?

Accepted Answer

Obligate anaerobe

Question 8

Which of the following is a direct method for measuring microbial growth?

Accepted Answer

Plate count

Question 9

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

Accepted Answer

Complex medium

Question 10

Which of the following best describes the function of reducing media?

Accepted Answer

To cultivate obligate anaerobes by removing oxygen

Question 11

A bacterial population starts with 100 cells and has a generation time of 30 minutes. How many cells will there be after 3 hours of exponential growth? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 100 	imes 2^6$ = 6400$$ cells

Question 12

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

Accepted Answer

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

Question 13

Which of the following is an example of a trace element required for microbial growth?

Accepted Answer

Iron (Fe)

Question 14

A microbiologist is using a spectrophotometer to estimate bacterial numbers in a culture. Which method is being used?

Accepted Answer

Turbidity measurement

Question 15

Which of the following best explains why obligate aerobes can survive in the presence of oxygen?

Accepted Answer

They possess both catalase and superoxide dismutase (SOD) to neutralize toxic oxygen species.

Question 16

Which of the following best describes the purpose of selective media?

Accepted Answer

To suppress unwanted microbes and encourage the growth of desired microbes

Question 17

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

Accepted Answer

150 bacteria per 100 mL

Question 18

Which of the following is NOT a characteristic of biofilms?

Accepted Answer

They are easily removed by antibiotics.

Question 19

Which of the following best describes the streak plate method?

Accepted Answer

It is used to isolate pure cultures by spreading bacteria over the surface of an agar plate.

Question 20

Which of the following is a correct statement about the Most Probable Number (MPN) method?

Accepted Answer

It estimates bacterial concentration by statistical analysis of positive growth in serial dilutions.

Microbial Growth: Requirements, Culture Media, and Measurement

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