Q: If you start with 2 bacterial cells and they undergo 4 rounds of binary fission, how many cells will you have at the end? 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.

$$N = 2 \times 2^4$ = 32$$ cells

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 then separates into two identical cells.

Question 2

If you start with 2 bacterial cells and they undergo 4 rounds of binary fission, how many cells will you have at the end? 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

$$N = 2 	imes 2^4$ = 32$$ cells

Question 3

Which phase of the microbial growth curve is characterized by maximum cell division and exponential increase in cell number?

Accepted Answer

Log (exponential) phase

Question 4

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

Accepted Answer

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

Question 5

Which type of microorganism would you expect to find thriving in a hot spring with temperatures around 75°C?

Accepted Answer

Thermophiles

Question 6

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

Accepted Answer

It 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 microbiologist wants to count the number of viable bacteria in a milk sample. Which method would be most appropriate?

Accepted Answer

Viable plate count assay

Question 9

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

Accepted Answer

Oxygen can generate toxic waste products that require special enzymes to neutralize.

Question 10

A laboratory is classified as BSL-3. Which of the following is most likely true about the microbes handled there?

Accepted Answer

They can cause serious or potentially lethal diseases via inhalation.

Question 11

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

Accepted Answer

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

Question 12

A sample of E. coli is filtered, and 275 colonies are obtained from 0.001 L. What is the concentration in cfu/L?

Accepted Answer

$$\frac{275}{0.001} = 275,000$$ cfu/L

Question 13

Which of the following is an example of a differential medium?

Accepted Answer

ChromAgar ECC, which distinguishes E. coli from other coliforms by color.

Question 14

Which environmental parameter is most likely to affect the osmotic pressure experienced by microbes in a laboratory medium?

Accepted Answer

Salt concentration

Question 15

Why is it important to control pH when culturing microbes in the lab?

Accepted Answer

Extreme pH can denature enzymes and inhibit microbial growth.

Question 16

Which of the following best describes a chemically defined medium?

Accepted Answer

A medium in which the exact chemical composition is known.

Question 17

A food recall is issued due to contamination with Listeria monocytogenes. Which growth characteristic of Listeria makes it a particular concern in refrigerated foods?

Accepted Answer

It can grow at low temperatures (psychrotroph).

Question 18

Which method would be most appropriate for estimating the number of bacteria in a turbid broth culture?

Accepted Answer

Measuring turbidity with a spectrophotometer (indirect method)

Question 19

Which of the following statements about MacConkey agar is correct?

Accepted Answer

It is both selective and differential.

Microbial Growth and Reproduction: Key Concepts and Laboratory Applications

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