Q: A culture of E. coli is incubated at 37°C and has a generation time of 30 minutes. How many cells will there be after 3 hours if you start with 100 cells?

$$N = 100 \times 2$$^{6}$$ = 6400$$

Question 1

Which phase of the bacterial growth curve is characterized by the synthesis of new enzymes and repair of cellular components, but little to no increase in cell number?

Accepted Answer

Lag phase

Question 2

A diabetic patient develops gas gangrene in a foot ulcer. Which property of Clostridium perfringens allows it to thrive in this environment?

Accepted Answer

It is a strict anaerobe and grows in dead, oxygen-depleted tissue.

Question 3

Which of the following best describes the effect of penicillin on bacterial cells?

Accepted Answer

Penicillin prevents cross-linking of peptidoglycan chains, weakening the cell wall during the log phase.

Question 4

Which equation correctly describes the number of bacteria after $$n$$ generations, starting from a single cell?

Accepted Answer

$$N = 2^n$$

Question 5

A culture of E. coli is incubated at 37°C and has a generation time of 30 minutes. How many cells will there be after 3 hours if you start with 100 cells?

Accepted Answer

$$N = 100 	imes 2$$^{6}$$ = 6400$$

Question 6

Which adaptation allows psychrophiles to survive and grow at temperatures below 0°C?

Accepted Answer

They possess cold-adapted proteins and antifreeze molecules.

Question 7

Which of the following statements about endospores is TRUE?

Accepted Answer

Endospores contain small acid-soluble proteins (SASPs) that protect DNA.

Question 8

Which of the following best explains why obligate anaerobes cannot survive in the presence of oxygen?

Accepted Answer

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

Question 9

A bacterium that grows optimally at pH 3 and cannot survive at neutral pH is classified as a(n):

Accepted Answer

Acidophile

Question 10

Which of the following best describes quorum sensing in bacteria?

Accepted Answer

It is the ability to sense population density via signal molecules and regulate gene expression.

Question 11

Which of the following is a correct statement about persister cells?

Accepted Answer

They are dormant variants of regular cells that are highly tolerant to antibiotics.

Question 12

Which of the following best explains why most bacteria do not grow below a water activity ($$a_w) of 0.9$$?

Accepted Answer

Low water activity causes dehydration and inhibits essential cellular processes.

Question 13

Which of the following is a compatible solute that bacteria may accumulate to survive in high-salt environments?

Accepted Answer

Glycine betaine

Question 14

A bacterium that grows in the presence or absence of oxygen, but does not use oxygen for metabolism, is classified as a(n):

Accepted Answer

Aerotolerant anaerobe

Question 15

Which of the following best describes the difference between growth rate and growth yield?

Accepted Answer

Growth rate is the speed of cell division during log phase; growth yield is the total cell number at stationary phase.

Question 16

Which of the following is a likely outcome if a nonhalophilic bacterium is placed in a high-salt environment?

Accepted Answer

The cell will lose water and may undergo plasmolysis.

Question 17

Which of the following is TRUE about viable but nonculturable (VBNC) cells?

Accepted Answer

They are alive but cannot be grown on routine lab media without an environmental trigger.

Question 18

Which of the following best explains why Deinococcus radiodurans is highly resistant to ionizing radiation?

Accepted Answer

It has multiple DNA repair systems and a tightly packed genome.

Question 19

Which of the following best describes the role of lysozyme in bacterial cell wall degradation?

Accepted Answer

Lysozyme breaks existing NAG-NAM bonds in peptidoglycan.

Question 20

A bacterium isolated from a hot spring grows optimally at 70°C. Which category does it belong to?

Accepted Answer

Thermophile

Microbial Growth and Environmental Adaptations: Study Notes for Microbiology

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