Q: Which equation correctly calculates the total number of bacterial cells after $$n$$ generations, starting with $$N_{initial}$$ cells?

$$N_{total} = N_{initial} \times 2^n$$

Question 1

Which of the following best describes the role of nitrogen fixation in microbial growth?

Accepted Answer

It reduces nitrogen gas ($$N_2) to $$ammonia ($$NH_4$$^+$$), making nitrogen biologically usable.

Question 2

A bacterial culture is placed in a liquid thioglycollate medium. Growth is observed only at the top of the tube. What does this indicate about the bacteria's oxygen requirements?

Accepted Answer

They are obligate aerobes.

Question 3

Which of the following statements about biofilms is TRUE?

Accepted Answer

Biofilms are complex aggregations of microorganisms that can form on medical devices and mucous membranes.

Question 4

During which phase of the bacterial growth curve are cells most susceptible to antibiotics, and why?

Accepted Answer

Logarithmic phase, because cells are actively dividing and metabolic activity is highest.

Question 5

A patient develops a persistent infection after receiving a urinary catheter. Which property of biofilms most likely contributes to the difficulty in treating this infection?

Accepted Answer

Biofilm cells are protected by an extracellular matrix and can share resistance genes.

Question 6

Which equation correctly calculates the total number of bacterial cells after $$n$$ generations, starting with $$N_{initial}$$ cells?

Accepted Answer

$$N_{total} = N_{initial} 	imes 2^n$$

Question 7

Which of the following best describes a chemoheterotroph?

Accepted Answer

An organism that uses organic compounds for both energy and carbon.

Question 8

A bacterium is classified as a mesophile. Which environment would it most likely thrive in?

Accepted Answer

The human body at $$37^\circC.$$

Question 9

Which of the following is a trace element required in small amounts for microbial growth?

Accepted Answer

Iron

Question 10

A culture of bacteria is placed in a hypertonic solution. What is the most likely outcome?

Accepted Answer

Cells will shrink due to water loss (plasmolysis), inhibiting growth.

Question 11

Which of the following best explains why bacterial endospores can survive for decades in dry environments?

Accepted Answer

Endospores are metabolically inactive and resistant to desiccation.

Question 12

Which of the following is NOT a function of the extracellular polymeric matrix in biofilms?

Accepted Answer

Increases susceptibility to antibiotics.

Question 13

A bacterial population starts with 100 cells. If the generation time is 30 minutes and the population grows for 3 hours, how many cells will be present at the end? Use $$N_{total} = N_{initial} 	imes 2^n.$$

Accepted Answer

6400 cells

Question 14

Which of the following best describes a facultative anaerobe?

Accepted Answer

An organism that can grow with or without oxygen, using aerobic respiration, fermentation, or anaerobic respiration.

Question 15

Which phase of the bacterial growth curve is characterized by equal rates of cell division and cell death?

Accepted Answer

Stationary phase

Question 16

Which of the following is a real-world example of a synergistic microbial relationship?

Accepted Answer

Corynebacterium species living in the eye, benefiting both the host and the microbe.

Question 17

Which of the following is a growth factor required by some bacteria because they cannot synthesize it themselves?

Accepted Answer

NADH

Question 18

Which method is used to indirectly estimate microbial population size by measuring turbidity?

Accepted Answer

Spectrophotometry

Question 19

Which of the following best describes the effect of temperature on bacterial cell membranes?

Accepted Answer

High temperatures make membranes too fluid, while low temperatures make them rigid and fragile.

Question 20

Which organism is most likely to thrive in an acidic environment with a pH of 2?

Accepted Answer

Acidophile

Microbial Nutrition and Growth: Study Guide

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