Question 1

Which phase of the standard bacterial growth curve is characterized by an equal rate of cell division and cell death, resulting in a constant number of live cells?

Accepted Answer

Stationary phase

Question 2

A microbiologist transfers 1 mL of a bacterial culture into 9 mL of sterile diluent. What is the dilution factor for this step?

Accepted Answer

$$1/10$$

Question 3

Why is the log phase preferred for experiments involving bacterial growth?

Accepted Answer

Bacterial growth occurs at an exponential rate and cells are most uniform

Question 4

Which of the following best describes the purpose of serial dilution in bacterial enumeration?

Accepted Answer

To reduce the number of bacteria to a countable range

Question 5

A student performs a serial dilution and plates 0.1 mL from the $$10^{-4}$$ dilution tube. After incubation, 150 colonies are counted. What is the CFU/mL in the original sample? Use the formula $$	ext{CFU/mL} = \frac{	ext{number of colonies}}{	ext{volume plated (mL)} 	imes 	ext{dilution factor}}.$$

Accepted Answer

$$1.5 	imes 10^6$ CFU/mL

Question 6

During which phase of the standard growth curve do bacteria acclimatize to a new environment without dividing?

Accepted Answer

Lag phase

Question 7

If a bacterial culture has a generation time of 20 minutes, how many generations will occur in 2 hours?

Accepted Answer

12

Question 8

Which of the following is NOT a reason why bacteria in nature do not follow the standard growth curve observed in the laboratory?

Accepted Answer

Constant temperature in nature

Question 9

A student performs three serial 1/10 dilutions. What is the final dilution factor relative to the original sample?

Accepted Answer

$$1/1000$$

Question 10

Which of the following best describes the spread plate technique?

Accepted Answer

Evenly distributing a liquid sample over the surface of an agar plate using a spreader

Question 11

If you count 234 colonies on a plate that received 0.1 mL of a $$10^{-5}$$ dilution, what is the CFU/mL in the original sample?

Accepted Answer

$$2.34 	imes 10^7$ CFU/mL

Question 12

Which phase of the bacterial growth curve is most likely to be observed when nutrients are depleted and waste products accumulate?

Accepted Answer

Stationary phase

Question 13

What is the main reason for using serial dilutions before plating a bacterial sample?

Accepted Answer

To obtain plates with a countable number of colonies

Question 14

A student observes that after several hours, the number of live bacteria in a culture is decreasing. Which phase of the growth curve is the culture most likely in?

Accepted Answer

Death phase

Question 15

Which of the following best defines 'generation time' in bacterial growth?

Accepted Answer

The time required for a single bacterial cell to divide into two cells

Question 16

If you plate 0.2 mL from a $$10^{-3}$$ dilution and count 80 colonies, what is the CFU/mL in the original sample?

Accepted Answer

$$4.0 	imes 10^5$ CFU/mL

Question 17

Which of the following is a correct statement about enumeration of bacteria using spread plates?

Accepted Answer

Each visible colony on the plate arises from a single viable cell or CFU

Question 18

A culture is in the log phase. If the initial population is $$1 	imes 10^3$ cells and the generation time is 30 minutes, how many cells will there be after 2 hours?

Accepted Answer

$$1.6 	imes 10^4$

Microbial Nutrition and Growth: Bacterial Enumeration, Growth Curves, and Serial Dilution

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