Question 1

A microbiologist is attempting to culture a newly discovered bacterium that grows optimally at 55°C and can survive in hot springs. Which classification best describes this organism based on its temperature preference?

Accepted Answer

Thermophile

Question 2

Which of the following best explains why salt is used to preserve foods such as meats and pickles?

Accepted Answer

Salt increases osmotic pressure, causing plasmolysis in bacteria.

Question 3

A bacterium is found to require oxygen for growth but is killed by atmospheric levels of oxygen. Which term best describes this organism?

Accepted Answer

Microaerophile

Question 4

Which of the following statements about agar is correct?

Accepted Answer

Agar is a complex polysaccharide derived from seaweed and is used to solidify culture media.

Question 5

A laboratory is attempting to isolate a pure culture from a mixed sample. Which method is most commonly used to achieve this?

Accepted Answer

Streak plate method

Question 6

Which of the following best describes the function of phosphate salts in bacterial culture media?

Accepted Answer

They serve as a buffer to maintain proper pH.

Question 7

A researcher is culturing a bacterium that cannot grow in the presence of oxygen. Which of the following best explains why this organism cannot survive in oxygenated environments?

Accepted Answer

It lacks enzymes to neutralize harmful forms of oxygen.

Question 8

Which of the following equations correctly represents the calculation of bacterial population size after $$n$$ generations, starting from a single cell, assuming binary fission?

Accepted Answer

$$N = 2^n$$

Question 9

A water sample is suspected to contain a low concentration of bacteria. Which direct method would be most appropriate for quantifying the bacteria in this sample?

Accepted Answer

Filtration

Question 10

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

Accepted Answer

The number of new cells equals the number of dying cells.

Question 11

A microbiologist is using a spectrophotometer to estimate bacterial growth in a liquid culture. Which property is being measured?

Accepted Answer

Turbidity

Question 12

Which of the following is a key difference between chemically defined media and complex media?

Accepted Answer

Chemically defined media contain precise amounts of pure chemicals, while complex media contain extracts from natural sources.

Question 13

A patient sample is suspected to contain a very small number of a specific pathogen. Which culture technique would be most effective for increasing the number of this pathogen to detectable levels?

Accepted Answer

Enrichment culture

Question 14

Which of the following best describes the process of lyophilization for preserving microbial cultures?

Accepted Answer

Removing water by high vacuum and quickly freezing at –54 to –72°C

Question 15

A bacterial culture is in the log phase of growth. Which of the following statements is true regarding the population at this stage?

Accepted Answer

The population is increasing at a constant, exponential rate.

Question 16

Which of the following is NOT a direct method for measuring microbial growth?

Accepted Answer

Turbidity

Question 17

A microbiologist is working with a bacterium that can grow in the presence or absence of oxygen, but produces more energy when oxygen is available. Which term best describes this organism?

Accepted Answer

Facultative anaerobe

Question 18

Which of the following best explains why logarithmic scales are used to plot bacterial growth curves?

Accepted Answer

They allow both very small and very large numbers to be displayed on the same graph.

Question 19

A sample of bacteria is diluted 1:1000 and 0.1 mL is plated. After incubation, 50 colonies are counted. What is the concentration of bacteria in the original sample (in CFU/mL)? Use the formula $$	ext{CFU/mL} = \frac{	ext{Number of colonies}}{	ext{Volume plated (mL)} 	imes 	ext{Dilution factor}}.$$

Accepted Answer

$$5 	imes 10^5$

Question 20

Which of the following best describes the role of reducing media in culturing anaerobic bacteria?

Accepted Answer

They remove oxygen from the media and culture environment.

Microbial Growth: Physical and Chemical Requirements, Culture Methods, and Measurement

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