Q: A culture starts with 5 bacterial cells. If the generation time is 20 minutes, how many cells will there be after 2 hours? Use the formula $$\text{Initial cells} \times 2$$^{\text{Number of generations}$$}.$$

$$5 \times 2$$^{6}$$ = 320$$ cells

Q: A sample is plated and 65 colonies are counted on a plate where 0.1 mL was plated from a 1:1000 dilution. What is the concentration of bacteria in the original sample? Use $$\text{cfu/mL} = \left(\frac{\# \text{cfu}}{\text{volume plated}}\right) \times \text{dilution factor}.$$

$$\left(\frac{65}{0.1}\right) \times 1000 = 650,000$$ cfu/mL

Question 1

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

Accepted Answer

The cell elongates, replicates its DNA, forms a cross-wall, and separates into two identical cells.

Question 2

A culture starts with 5 bacterial cells. If the generation time is 20 minutes, how many cells will there be after 2 hours? Use the formula $$	ext{Initial cells} 	imes 2$$^{	ext{Number of generations}$$}.$$

Accepted Answer

$$5 	imes 2$$^{6}$$ = 320$$ cells

Question 3

Which phase of the microbial growth curve is characterized by the highest rate of cell division?

Accepted Answer

Log (exponential) phase

Question 4

A sample is plated and 65 colonies are counted on a plate where 0.1 mL was plated from a 1:1000 dilution. What is the concentration of bacteria in the original sample? Use $$	ext{cfu/mL} = \left(\frac{\# 	ext{cfu}}{	ext{volume plated}}ight) 	imes 	ext{dilution factor}.$$

Accepted Answer

$$\left(\frac{65}{0.1}ight) 	imes 1000 = 650,000$$ cfu/mL

Question 5

Which type of microorganism would most likely be found growing in a hot spring at 90°C?

Accepted Answer

Hyperthermophile

Question 6

Why is agar commonly used as a solidifying agent in microbiological media?

Accepted Answer

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

Question 7

Which of the following best describes a selective medium?

Accepted Answer

A medium that inhibits the growth of some microbes while allowing others to grow.

Question 8

A water sample is filtered and 200 colonies are counted from 0.5 L of water. What is the concentration of bacteria in the water? Use $$	ext{cfu/L} = \frac{\# 	ext{cfu}}{	ext{volume plated}}.$$

Accepted Answer

$$\frac{200}{0.5} = 400$$ cfu/L

Question 9

Which of the following is a reason why oxygen can be toxic to some microbes?

Accepted Answer

Oxygen leads to the formation of toxic waste products that require special enzymes to neutralize.

Question 10

Which of the following best describes the stationary phase of the microbial growth curve?

Accepted Answer

Microbes are dying at a rate equal to the rate of new cell formation.

Question 11

A microbiologist wants to count only live bacteria in a sample. Which method should they use?

Accepted Answer

Viable plate count assay

Question 12

Which of the following best explains why Listeria monocytogenes contamination in ice cream is a public health concern?

Accepted Answer

Listeria can grow at refrigeration temperatures and cause disease in humans.

Question 13

Which of the following is NOT a parameter that must be controlled to grow microbes in the lab?

Accepted Answer

Light intensity

Question 14

Which type of culture medium contains yeast extract and other complex ingredients, but not all components are chemically defined?

Accepted Answer

Chemically complex medium

Question 15

Which of the following best describes the use of turbidity to measure microbial growth?

Accepted Answer

It measures the cloudiness of a broth to estimate cell density.

Question 16

Which biosafety level (BSL) laboratory is required for handling the most dangerous pathogens, such as Ebola virus?

Accepted Answer

BSL-4

Question 17

Which of the following scenarios best illustrates the application of a differential medium?

Accepted Answer

A medium that changes color when bacteria ferment a specific sugar.

Question 18

Which of the following is a correct statement about the death phase in the microbial growth curve?

Accepted Answer

The number of dying cells exceeds the number of new cells formed.

Microbial Growth and Reproduction: Key Concepts and Laboratory Applications

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