Question 1

Which of the following best describes a chemoheterotroph?

Accepted Answer

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

Question 2

Why is oxygen deadly for obligate anaerobes?

Accepted Answer

They lack the enzymes necessary to detoxify reactive oxygen species.

Question 3

Which enzyme catalyzes the reaction $$2 O_2$^- + 2 H^+ \rightarrow H_2O_2 + O_2$?

Accepted Answer

Superoxide dismutase

Question 4

A bacterium grows only at the bottom of a thioglycollate broth tube. What is its oxygen requirement?

Accepted Answer

Obligate anaerobe

Question 5

Nitrogen fixation is essential to life on Earth because:

Accepted Answer

It converts nitrogen gas into ammonia, making nitrogen available to living organisms.

Question 6

Which of the following is a growth factor?

Accepted Answer

Amino acids that an organism cannot synthesize

Question 7

What happens to the cell membrane of a bacterium at temperatures above its optimum growth temperature?

Accepted Answer

It becomes too fluid and may lose integrity.

Question 8

Which type of microorganism would most likely be found in a hot spring at 90°C?

Accepted Answer

Hyperthermophile

Question 9

A bacterium that grows best at pH 7 is classified as a:

Accepted Answer

Neutrophile

Question 10

Which of the following best explains why most cells die in the absence of water?

Accepted Answer

Water is an important reactant in many metabolic reactions.

Question 11

A bacterium that can survive in high salt concentrations is called a(n):

Accepted Answer

Obligate halophile

Question 12

Which of the following is an example of a synergistic relationship?

Accepted Answer

Two bacteria produce more biofilm together than alone.

Question 13

Biofilms are more harmful than free-living bacteria because:

Accepted Answer

They form complex communities that protect bacteria from environmental stresses.

Question 14

Which of the following is true about defined (synthetic) media?

Accepted Answer

The exact chemical composition is known.

Question 15

Blood agar is an example of which type of medium?

Accepted Answer

Differential medium

Question 16

Which of the following best describes the function of reducing media?

Accepted Answer

They remove free oxygen from the medium to support the growth of obligate anaerobes.

Question 17

If a bacterial culture has a generation time of 30 minutes, how many cells will there be after 2 hours if you start with 1 cell? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

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

Question 18

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

Accepted Answer

Log (exponential) phase

Question 19

Which of the following best explains why MacConkey agar is both selective and differential?

Accepted Answer

It contains bile salts and crystal violet to inhibit Gram-positive bacteria and lactose to differentiate fermenters.

Question 20

A patient has a wound infection with bacteria that grow only in the absence of oxygen. Which culture method and medium would be most appropriate to isolate this organism?

Accepted Answer

Anaerobic jar with reducing medium

Microbial Nutrition and Growth: Study Notes

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