Q: A sample contains 1,000 bacteria. If the generation time is 30 minutes, how many bacteria will be present after 2 hours of exponential growth? Use the formula $$N = N_0$ \times 2^n$$, where $$n is $$the number of generations.

$$N = 1,000 \times 2^4$ = 16,000$$

Question 1

Which of the following best describes a chemoheterotroph?

Accepted Answer

An organism that uses organic compounds as both an energy and carbon source.

Question 2

A microbiologist is culturing a bacterium that cannot survive in the presence of oxygen. Which of the following enzymes is this organism most likely to lack?

Accepted Answer

Catalase

Question 3

Which phase of the microbial growth curve is characterized by the highest susceptibility to antimicrobial drugs?

Accepted Answer

Log (exponential) phase

Question 4

A bacterium isolated from a hot spring grows optimally at 90$$^\circC. $$How would you classify this organism?

Accepted Answer

Hyperthermophile

Question 5

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

Accepted Answer

They lack enzymes to detoxify reactive oxygen species.

Question 6

A microbiologist wants to isolate a pure culture of a bacterium from a mixed sample. Which technique should she use?

Accepted Answer

Streak plate method

Question 7

Which of the following is a trace element required by microorganisms?

Accepted Answer

Iron (Fe)

Question 8

A bacterium that grows equally well with or without oxygen is classified as:

Accepted Answer

Aerotolerant anaerobe

Question 9

Which of the following best describes the function of quorum sensing in biofilms?

Accepted Answer

It allows bacteria to coordinate gene expression based on population density.

Question 10

A sample contains 1,000 bacteria. If the generation time is 30 minutes, how many bacteria will be present after 2 hours of exponential growth? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 1,000 	imes 2^4$ = 16,000$$

Question 11

Which type of culture medium would you use to isolate Neisseria gonorrhoeae, a capnophile, from a clinical specimen?

Accepted Answer

A CO$$_2$$ incubator with selective medium

Question 12

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

Accepted Answer

Conversion of atmospheric N$$_2 to $$ammonia (NH$$_3) $$for biosynthesis

Question 13

A microbiologist uses a spectrophotometer to measure the turbidity of a broth culture. What is she indirectly measuring?

Accepted Answer

The population size of the culture

Question 14

Which of the following is NOT a function of microbial biofilms?

Accepted Answer

Increasing susceptibility to antibiotics

Question 15

Which of the following best explains why Mycobacterium tuberculosis can survive for months in dry conditions?

Accepted Answer

It has a cell wall that retains water.

Question 16

Which of the following media would be most appropriate to isolate Gram-negative bacteria from a mixed sample?

Accepted Answer

Selective medium containing bile salts and crystal violet

Question 17

A scientist is studying a bacterium that grows best at pH 9.0. This organism is most likely a(n):

Accepted Answer

Alkalinophile

Question 18

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

Accepted Answer

Defined media have a known chemical composition; complex media do not.

Question 19

Which of the following methods would be most appropriate for estimating the number of viable bacteria in a water sample with low population density?

Accepted Answer

Membrane filtration

Microbial Nutrition, Growth, and Culturing: Chapter 6 Study Notes

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