Question 1

Which of the following best describes the difference between defined and complex media in microbiology?

Accepted Answer

Defined media has an exact chemical composition known, while complex media contains extracts of yeast and meat.

Question 2

A microbiologist wants to culture a bacterium that cannot synthesize certain amino acids. Which type of nutrient is this bacterium dependent on?

Accepted Answer

Growth factors

Question 3

Which of the following is the correct formula for calculating the number of generations ($$n) in a $$bacterial culture, given the initial cell number ($$N_0) $$and final cell number ($$N$$)?

Accepted Answer

$$n = \log_2$ \left( \frac{N}{N_0$} \right)$$

Question 4

Which phase of the microbial growth curve is characterized by maximum metabolic activity and highest sensitivity to antibiotics?

Accepted Answer

Exponential (log) phase

Question 5

A sample is diluted $$10^{-6}$$ and 234 colonies are counted on a plate. What is the original concentration of cells in CFU/mL?

Accepted Answer

$$2.34 	imes 10^8$ CFU/mL

Question 6

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms are less likely to form on surfaces exposed to water.

Question 7

Which enzyme protects aerobic microbes from the toxic effects of hydrogen peroxide ($$H_2O_2$$)?

Accepted Answer

Catalase

Question 8

Which group of microbes would most likely thrive at a pH of 9?

Accepted Answer

Alkaliphiles

Question 9

What is the main reason why viable plate counts are considered more sensitive than direct microscopic counts?

Accepted Answer

They only count living cells capable of forming colonies.

Question 10

Which of the following best describes the function of magnesium ions ($$Mg^{2+}) in $$microbial cells?

Accepted Answer

Stabilizes ribosomes, membranes, and nucleic acids

Question 11

A microbiologist wants to sterilize a solution that is heat-sensitive. Which method is most appropriate?

Accepted Answer

Filtration through a $$0.2\ \mum $$membrane

Question 12

Which of the following is a compatible solute used by microbes to prevent water loss in high-salt environments?

Accepted Answer

Glycine betaine

Question 13

Which temperature class includes most human pathogens?

Accepted Answer

Mesophiles

Question 14

Which of the following best explains why the stationary phase occurs in a batch culture?

Accepted Answer

Nutrients are depleted and waste products accumulate.

Question 15

Which of the following is the correct definition of generation time ($$g) in $$microbiology?

Accepted Answer

The time required for the population to double

Question 16

Which of the following statements about autoclaving is TRUE?

Accepted Answer

It sterilizes by using steam under pressure at $$121^\circC $$for 15 minutes.

Question 17

A bacterium isolated from a hot spring grows optimally at $$90^\circC. $$Which temperature class does it belong to?

Accepted Answer

Hyperthermophile

Question 18

Which of the following best describes the role of iron (Fe) in microbial cells?

Accepted Answer

Required for electron transport

Question 19

Which of the following is a key difference between binary fission and budding in microbial cell division?

Accepted Answer

Binary fission results in equal division, while budding results in unequal division.

Question 20

Which of the following best describes the function of a chemostat in microbial culture?

Accepted Answer

It maintains steady-state exponential growth by continuously adding nutrients and removing waste.

Microbial Growth: Requirements, Measurement, and Control

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