Question 1

Which phase of microbial growth is most sensitive to antimicrobial agents, and why?

Accepted Answer

Log (exponential) phase, because cells are actively dividing and have high metabolic activity.

Question 2

A clinical sample is collected from a patient suspected of having a bacterial infection. Why is it important to avoid contamination during sampling, and what is the most likely consequence if contamination occurs?

Accepted Answer

Contamination can introduce non-pathogenic microbes, leading to false positive results and misdiagnosis.

Question 3

Which of the following best describes the difference between arithmetic and logarithmic growth in microbial populations?

Accepted Answer

Arithmetic growth results in a constant increase in cell number, while logarithmic growth results in exponential increase.

Question 4

A bacterium is classified as an obligate aerobe. Which of the following statements is TRUE regarding its oxygen requirements?

Accepted Answer

It requires oxygen as the final electron acceptor in its electron transport chain.

Question 5

Which enzyme is responsible for detoxifying superoxide radicals ($O_2^-$) in aerobic bacteria?

Accepted Answer

Superoxide dismutase (SOD)

Question 6

A microbe is found growing in a hot spring at 70°C. Which term best describes its temperature classification?

Accepted Answer

Thermophile

Question 7

Which of the following statements about biofilms is CORRECT?

Accepted Answer

Biofilms are communities of microorganisms attached to a surface and embedded in a self-produced matrix.

Question 8

Which of the following media types would you use to distinguish between two species of bacteria based on their metabolic properties?

Accepted Answer

Differential media

Question 9

A bacterium is classified as a facultative anaerobe. Which of the following best describes its growth pattern in a test tube of thioglycollate broth?

Accepted Answer

Growth throughout the tube, but more dense at the top due to preference for aerobic respiration.

Question 10

Which chemical requirement is essential for the synthesis of nucleic acids and phospholipids in microbes?

Accepted Answer

Phosphorus

Question 11

A microbe is described as a chemoheterotroph. What does this mean regarding its energy and carbon sources?

Accepted Answer

It uses organic compounds for both energy and carbon.

Question 12

Which of the following is a common misconception about pure cultures in microbiology?

Accepted Answer

Pure cultures are always representative of natural microbial communities.

Question 13

Why are most bacteria unable to grow in highly acidic or highly alkaline environments?

Accepted Answer

Extreme pH disrupts hydrogen bonding in proteins and enzymes, affecting their activity.

Question 14

Which of the following is NOT a function of water in microbial cells?

Accepted Answer

Acting as the final electron acceptor in aerobic respiration.

Question 15

A patient develops a persistent infection on a medical implant. Which microbial property is most likely responsible for the difficulty in treating this infection?

Accepted Answer

The bacteria form a biofilm, which protects them from antibiotics and the immune system.

Question 16

Which of the following best explains why obligate anaerobes are killed by exposure to oxygen?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 17

A bacterium is grown in a defined medium containing only glucose as a carbon source and ammonium chloride as a nitrogen source. Which term best describes this medium?

Accepted Answer

Defined (synthetic) medium

Question 18

Which of the following growth factors is required for the synthesis of NADH in microbial cells?

Accepted Answer

Nicotinic acid (niacin)

Question 19

A microbe is classified as an aerotolerant anaerobe. Which statement best describes its oxygen tolerance?

Accepted Answer

It grows equally well with or without oxygen but does not use oxygen for metabolism.

Question 20

Which of the following equations best represents the exponential growth of a bacterial population, where $N_t$ is the number of cells at time $t$, $N_0$ is the initial number of cells, and $n$ is the number of generations?

Accepted Answer

$N_t = N_0 	imes 2^n$

Microbial Nutrition, Growth, and Biofilms: Study Notes for MIC 205

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