Question 1

Which of the following best describes an obligate anaerobe?

Accepted Answer

Requires absence of oxygen and lacks both catalase and peroxidase.

Question 2

A microbe is found to grow in the presence and absence of oxygen, but grows best when oxygen is available. Which category does it belong to?

Accepted Answer

Facultative anaerobe

Question 3

Which enzyme catalyzes the conversion of superoxide radical $$O_2$$^{-}$$ to hydrogen peroxide H_2O_2$?

Accepted Answer

Superoxide dismutase

Question 4

Why is molecular oxygen ($$O_2) $$toxic to some microbes?

Accepted Answer

Because $$O_2$$ can pick up electrons and form reactive oxygen species that damage cellular components.

Question 5

Which of the following is NOT a macronutrient required for microbial growth?

Accepted Answer

Potassium

Question 6

A culture medium that contains high nutrient components such as brain heart infusion is best described as:

Accepted Answer

Complex medium

Question 7

During which phase of the bacterial growth curve do cells divide at a constant, maximum rate?

Accepted Answer

Log phase

Question 8

If a bacterial population doubles every 30 minutes, what is the generation time?

Accepted Answer

$$30$$ minutes

Question 9

Which trace element is considered a micronutrient for microbial growth?

Accepted Answer

Iron

Question 10

A selective medium is designed to:

Accepted Answer

Select for the survival of one type of microbe by inhibiting others.

Question 11

Which of the following best explains why the alcohol content in wine rarely exceeds 15%?

Accepted Answer

Alcohol becomes toxic to yeast cells, halting their growth.

Question 12

Which phase of the growth curve is characterized by no net increase in cell number due to nutrient depletion or accumulation of toxic products?

Accepted Answer

Stationary phase

Question 13

A microbe that grows optimally at high osmotic pressure and high salt concentrations is called:

Accepted Answer

Extreme halophile

Question 14

Which of the following equations correctly represents the action of catalase?

Accepted Answer

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 15

Which of the following would you expect to find in a microbe that can tolerate but not use oxygen?

Accepted Answer

SOD and peroxidase

Question 16

A streak plate is primarily used for which purpose in microbiology?

Accepted Answer

To isolate pure bacterial cultures.

Question 17

Which of the following best describes the death phase in a bacterial growth curve?

Accepted Answer

Cells are dying logarithmically, rate dependent on conditions.

Question 18

Which environmental condition would most likely favor the growth of thermophiles?

Accepted Answer

High temperature

Question 19

Which of the following is a reason why some microbes require trace elements such as selenium?

Accepted Answer

They serve as cofactors for enzymatic reactions.

Question 20

A differential medium is designed to:

Accepted Answer

Allow agents in the medium to differentiate between microbes based on appearance.

Microbial Growth: Environmental Requirements, Oxygen, and Growth Dynamics ~ Chp 6

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