Question 1

Which of the following best describes a biofilm?

Accepted Answer

A collection of microorganisms living on a surface and within a complex, synergistic community.

Question 2

A bacterium that uses light as its energy source and CO$$_2 as $$its carbon source is classified as which of the following?

Accepted Answer

Photoautotroph

Question 3

Which enzyme is essential for an organism to survive in the presence of superoxide radicals ($$O_2$$^-$$)?

Accepted Answer

Superoxide dismutase

Question 4

A Gram-positive bacterium is isolated from a salty environment, grows in clusters, ferments mannitol, and is a facultative anaerobe. Which of the following best describes this organism?

Accepted Answer

Halophilic, facultative anaerobe

Question 5

Which of the following statements about nitrogen is TRUE for most bacteria?

Accepted Answer

Nitrogen fixation by certain bacteria is essential for converting N$$_2 to $$ammonia.

Question 6

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

Accepted Answer

They lack enzymes to detoxify reactive oxygen species.

Question 7

A bacterial culture has a starting population of 1,000 cells. If the generation time is 30 minutes, how many cells will there be after 3 hours of exponential growth? Use the formula $$B = b 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

64,000

Question 8

Which of the following best describes a mesophile?

Accepted Answer

An organism that grows best between 20$$^\circC $$and 40$$^\circC$$

Question 9

Which of the following is a direct method for measuring microbial population size that does NOT require incubation?

Accepted Answer

Petroff-Hauser counting chamber

Question 10

A culture of bacteria is growing in a medium with a high concentration of salt. Which of the following terms best describes this environment?

Accepted Answer

Hypertonic

Question 11

Which of the following is a function of quorum sensing in bacterial biofilms?

Accepted Answer

It allows bacteria to detect and respond to population density by altering gene expression.

Question 12

Which of the following best explains why food preserved with high concentrations of salt or sugar resists microbial growth?

Accepted Answer

High salt or sugar creates a hypertonic environment, drawing water out of microbial cells and inhibiting growth.

Question 13

A bacterium that can survive in the presence of oxygen but does not use it for metabolism is best described as a(n):

Accepted Answer

Aerotolerant anaerobe

Question 14

Which of the following growth phases is characterized by a plateau in the number of living bacterial cells due to nutrient depletion and waste accumulation?

Accepted Answer

Stationary phase

Question 15

Which of the following is an example of an indirect method for estimating microbial population size?

Accepted Answer

Turbidity measurement using a spectrophotometer

Question 16

A bacterial culture has a generation time ($$G) of 40 $$minutes. If the culture is incubated for 4 hours, how many generations ($$n) $$have occurred? Use the formula $$G = \frac{t}{n}.$$

Accepted Answer

$$n = 6$$

Question 17

Which of the following best describes a psychrophile?

Accepted Answer

An organism that grows best at temperatures below 15$$^\circC$$

Question 18

Which of the following is a major reason why biofilms are more resistant to antibiotics than planktonic (free-living) bacteria?

Accepted Answer

Biofilms have a protective extracellular matrix and altered gene expression.

Question 19

Which of the following is NOT a chemical requirement for microbial growth?

Accepted Answer

Osmotic pressure

Question 20

A culture of E. coli has a starting population of 2 cells and a generation time of 20 minutes. How many cells will there be after 2 hours? Use $$B = b 	imes 2^n.$$

Accepted Answer

256

Chapter 6: Growth of Microbial Populations – Study Notes

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