Question 1

Which of the following best describes the role of trace elements in microbial growth?

Accepted Answer

They function as enzyme cofactors and are required in small amounts.

Question 2

A microbiologist is culturing a bacterium that requires many specific vitamins and amino acids to grow. Which type of medium should be used?

Accepted Answer

Chemically defined medium

Question 3

Which of the following statements about obligate anaerobes is correct?

Accepted Answer

They are unable to use oxygen and are often harmed by it.

Question 4

A bacterial culture is growing in a medium with a pH of 5.0, high salt concentration, and at 37°C. Which physical requirement is most likely limiting the growth of a typical non-extremophilic bacterium?

Accepted Answer

Osmotic pressure

Question 5

Which of the following equations correctly represents the calculation of the number of generations ($$n) in a $$bacterial culture, given the initial number of cells ($$N_0) $$and the final number of cells ($$N$$)?

Accepted Answer

$$n = \frac{\log N - \log N_0$}{\log 2}$$

Question 6

A researcher wants to isolate a pure culture of a bacterium from a mixed sample. Which method should be used and why?

Accepted Answer

Streak plate method, because it separates individual cells to form isolated colonies.

Question 7

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

Accepted Answer

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

Question 8

A sample of lake water is filtered to collect bacteria, and the filter is then placed on nutrient agar. What is the primary advantage of this method for counting bacteria?

Accepted Answer

It is effective for samples with low bacterial concentrations, concentrating bacteria from large volumes.

Question 9

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

Accepted Answer

The rate of cell division equals the rate of cell death.

Question 10

A microbiologist is using a spectrophotometer to measure the turbidity of a bacterial culture. What is being estimated by this method?

Accepted Answer

The total biomass, including both live and dead cells

Question 11

Which of the following best distinguishes selective media from differential media?

Accepted Answer

Selective media suppress unwanted microbes and encourage desired ones, while differential media distinguish between different microbes based on colony appearance.

Question 12

A bacterium is classified as a microaerophile. Which environment would best support its growth?

Accepted Answer

An environment with lower than atmospheric oxygen concentration

Question 13

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

Accepted Answer

It uses a statistical approach based on the number of positive tubes in dilution series.

Question 14

Which of the following best explains why fastidious organisms require chemically defined media?

Accepted Answer

They require many specific nutrients that must be provided in known amounts.

Question 15

A culture medium contains sodium thioglycolate. What type of bacteria is this medium designed to cultivate?

Accepted Answer

Obligate anaerobes

Question 16

Which of the following is a correct application of the streak plate method?

Accepted Answer

To isolate pure colonies from a mixed culture

Question 17

A bacterial culture is in the log (exponential) phase of growth. Which of the following best describes what is happening at this stage?

Accepted Answer

Cells are dividing at the fastest, most constant rate.

Question 18

Which of the following is a correct formula for calculating the number of bacteria per milliliter using a direct microscopic count with a Petroff-Hausser cell counter?

Accepted Answer

$$	ext{Number of bacteria/ml} = \frac{	ext{Number of cells counted}}{	ext{Volume of area counted}}$$

Question 19

Which of the following best describes the purpose of enrichment culture?

Accepted Answer

To increase the number of a desired microbe to detectable levels

Microbial Growth: Physical and Chemical Requirements

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