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 bacterium is found growing only at the bottom of a thioglycollate broth tube. What is the most likely classification of this organism with respect to oxygen?

Accepted Answer

Obligate anaerobe

Question 3

Which reactive oxygen species is detoxified by the enzyme catalase?

Accepted Answer

Hydrogen peroxide ($$H_2O_2)$$

Question 4

Nitrogen fixation is essential for life because:

Accepted Answer

It converts $$N_2$$ into usable forms like $$NH_3$$ for biosynthesis.

Question 5

Which of the following best explains why agar is used as a solidifying agent in microbiological media?

Accepted Answer

It melts at 100$$^	ext{o}C $$and solidifies below 40$$^	ext{o}C$$, and most microbes cannot digest it.

Question 6

A bacterium that grows optimally at 70$$^	ext{o}C $$would be classified as a:

Accepted Answer

Thermophile

Question 7

Which of the following media would best allow you to distinguish between bacteria that can ferment lactose and those that cannot?

Accepted Answer

Differential medium

Question 8

A microbiologist wants to count the number of viable bacteria in a water sample with very low bacterial density. Which method is most appropriate?

Accepted Answer

Membrane filtration followed by incubation

Question 9

During which phase of the bacterial growth curve are cells most susceptible to antibiotics that target cell wall synthesis?

Accepted Answer

Log (exponential) phase

Question 10

A culture medium contains 7.5% NaCl. Which group of organisms is most likely to grow in this medium?

Accepted Answer

Obligate halophiles

Question 11

Which of the following best describes the function of NADH in microbial metabolism?

Accepted Answer

Electron carrier in metabolic reactions

Question 12

A scientist wants to preserve a bacterial culture for decades without significant loss of viability. Which method should be used?

Accepted Answer

Lyophilization

Question 13

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

Accepted Answer

Microscopic count using a Petroff-Hausser chamber

Question 14

A bacterial culture is in stationary phase. Which of the following best describes what is happening?

Accepted Answer

The rate of cell division equals the rate of cell death.

Question 15

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

Accepted Answer

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

Question 16

A microbiologist streaks a plate to obtain isolated colonies. What is the primary purpose of this technique?

Accepted Answer

To obtain a pure culture from a mixed population

Question 17

Which of the following best describes the relationship between temperature and microbial growth rate?

Accepted Answer

Growth rate increases with temperature up to an optimum, then rapidly declines.

Question 18

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

Accepted Answer

Iron (Fe)

Question 19

A scientist measures the turbidity of a bacterial culture using a spectrophotometer. What is being estimated?

Accepted Answer

The total cell density (living and dead cells)

Question 20

Which of the following best describes a biofilm?

Accepted Answer

A complex community of microorganisms attached to a surface and encased in a protective matrix

Microbial Nutrition and Growth: Study Notes for Microbiology Students

Study Guide - Practice Questions

Study Guide - Flashcards