Question 1

Which of the following best describes the difference between chemically defined media and complex media used for microbial growth?

Accepted Answer

Chemically defined media have precisely known chemical composition, while complex media contain extracts with unknown exact composition.

Question 2

A bacterium is found growing in a hot spring at 80°C. Which term best describes this organism?

Accepted Answer

Hyperthermophile

Question 3

Which of the following is a direct method for measuring microbial growth?

Accepted Answer

Counting colonies on an agar plate

Question 4

Why do obligate anaerobes die in the presence of oxygen?

Accepted Answer

They lack the enzymes to neutralize toxic forms of oxygen such as superoxide radicals.

Question 5

Which of the following best explains why salted fish and honey are resistant to microbial spoilage?

Accepted Answer

High salt or sugar concentrations create a hypertonic environment, causing plasmolysis in microbial cells.

Question 6

A culture medium contains the following: glucose, ammonium phosphate, sodium chloride, magnesium sulfate, and water. This medium is best described as:

Accepted Answer

Chemically defined medium

Question 7

Which phase of the bacterial growth curve is characterized by intense metabolic activity but little to no cell division?

Accepted Answer

Lag phase

Question 8

A facultative halophile is best described as an organism that:

Accepted Answer

Can grow in the presence or absence of high salt concentrations.

Question 9

Which of the following equations correctly expresses the number of cells after $$n$$ generations, starting from a single cell?

Accepted Answer

$$N = 2^n$$

Question 10

Which of the following statements about Streptomyces is TRUE?

Accepted Answer

They are filamentous, gram-positive bacteria that produce asexual spores and antibiotics.

Question 11

Which of the following best describes the role of superoxide dismutase (SOD) in bacteria?

Accepted Answer

It neutralizes superoxide radicals to less toxic molecules.

Question 12

A bacterium that grows only at the bottom of a test tube of solid medium is most likely:

Accepted Answer

Obligate anaerobe

Question 13

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

Accepted Answer

Temperature

Question 14

Which of the following best explains why microaerophiles grow only in low oxygen concentrations?

Accepted Answer

They are sensitive to superoxide radicals and peroxides produced at higher oxygen concentrations.

Question 15

Which of the following is a real-life application of controlling osmotic pressure to prevent microbial growth?

Accepted Answer

Preserving meat with high concentrations of salt

Question 16

Which of the following statements about the stationary phase of bacterial growth is correct?

Accepted Answer

The number of new cells formed equals the number of cells dying.

Question 17

Which of the following is an example of an organic growth factor required by some bacteria?

Accepted Answer

Amino acids

Question 18

A scientist wants to culture a bacterium that requires a vitamin it cannot synthesize. What type of medium should be used?

Accepted Answer

A medium supplemented with the required vitamin

Question 19

Which of the following best describes the log phase of bacterial growth?

Accepted Answer

Cells are dividing at a constant, exponential rate.

Question 20

If a bacterial culture has a generation time of 30 minutes, how many cells will there be after 3 hours starting from a single cell? Use $$N = 2^n$$ where $$n is $$the number of generations.

Accepted Answer

64

Microbial Growth: Physical and Chemical Requirements, Culture Media, and Growth Dynamics

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