Q: A bacterial culture starts with 200 cells and has a generation time of 30 minutes. If the culture grows exponentially for 3 hours, how many cells will be present at the end? Use the formula $$N = N_0$ \times 2^n$$, where $$N_0 is $$the initial number of cells and $$n is $$the number of generations.

$$N = 200 \times 2^6$ = 12,800$$ cells

Question 1

A bacterial culture starts with 200 cells and has a generation time of 30 minutes. If the culture grows exponentially for 3 hours, how many cells will be present at the end? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N_0 is $$the initial number of cells and $$n is $$the number of generations.

Accepted Answer

$$N = 200 	imes 2^6$ = 12,800$$ cells

Question 2

Which of the following best describes the growth pattern of obligate anaerobes in a deep agar tube where oxygen is only present at the top?

Accepted Answer

They grow only at the bottom of the tube, away from oxygen.

Question 3

Which enzyme is responsible for converting hydrogen peroxide ($$H_2O_2) $$into water and oxygen, thereby protecting bacteria from oxidative damage?

Accepted Answer

Catalase

Question 4

A microbiologist wants to count only live bacterial cells in a culture. Which method should they use?

Accepted Answer

Serial dilution and plate count

Question 5

Which of the following best describes the stationary phase of bacterial growth in a broth culture?

Accepted Answer

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

Question 6

Which group of bacteria would you expect to find growing optimally at temperatures above $$80^\circC$$?

Accepted Answer

Hyperthermophiles

Question 7

A bacterial colony on a solid medium is observed to have older cells in the center and younger cells at the edge. What is the most likely explanation for this observation?

Accepted Answer

Cells in the center divided first and new cells spread outward as the colony grew.

Question 8

Which of the following is a growth factor that some bacteria require in their medium because they cannot synthesize it themselves?

Accepted Answer

Amino acids

Question 9

A facultative anaerobe is inoculated into a deep agar tube. Where would you expect to see growth?

Accepted Answer

Throughout the tube, but more growth at the top where oxygen is present.

Question 10

Which of the following best explains why iron is essential for bacterial growth and how bacteria acquire it in low-iron environments?

Accepted Answer

Iron is a cofactor for many enzymes, and bacteria secrete siderophores to bind and import iron.

Question 11

Which of the following best describes the function of superoxide dismutase in bacteria?

Accepted Answer

It converts superoxide radicals ($$O_2$$^-$$) into hydrogen peroxide (H_2O_2$).

Question 12

A culture medium is adjusted to a pH of 3.5. Which type of bacteria would most likely thrive in this environment?

Accepted Answer

Acidophiles

Question 13

Which of the following statements about bacterial exponential growth is correct?

Accepted Answer

The population doubles with each generation, following $$N = N_0$ 	imes 2^n.$$

Question 14

A researcher wants to measure the turbidity of a bacterial culture to estimate cell density. Which instrument should they use?

Accepted Answer

Spectrophotometer

Question 15

Which of the following best describes the lag phase of bacterial growth in a liquid culture?

Accepted Answer

Cells are metabolically active but not dividing rapidly as they adapt to new conditions.

Question 16

Which of the following would you add to a culture medium to encourage the growth of halophiles?

Accepted Answer

High concentrations of NaCl (salt)

Question 17

Which phase of bacterial growth is characterized by the highest sensitivity to antimicrobial agents?

Accepted Answer

Exponential (log) phase

Question 18

A bacterium is classified as a microaerophile. Where would you expect it to grow in a deep agar tube?

Accepted Answer

Just below the surface, where oxygen concentration is lower than at the top.

Question 19

Which of the following is a toxic form of oxygen that can damage bacterial cells?

Accepted Answer

Superoxide ($$O_2$$^-$$)

Question 20

A psychrotroph is isolated from spoiled refrigerated food. What is the most likely temperature range for its optimal growth?

Accepted Answer

$$0^\circC to$$ $$30^\circC$$

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