Q: A scientist observes that a bacterial population doubles every 30 minutes. If she starts with 1,000 cells, how many cells will there be after 2 hours? Use the formula $$N = N_0$ \times 2^n$$, where $$n is $$the number of generations.

$$N = 1,000 \times 2^4$ = 16,000$$

Question 1

Which of the following best describes the optimum growth temperature for a microorganism?

Accepted Answer

The temperature at which the organism grows most rapidly

Question 2

A food processing plant stores its products at $$4^{\circ}C$ to prevent spoilage. However, some spoilage still occurs. Which group of microorganisms is most likely responsible?

Accepted Answer

Psychrotrophs

Question 3

Which of the following statements about osmotic pressure and microbial cells is correct?

Accepted Answer

Facultative halophiles can tolerate salt concentrations between 2% and 15%

Question 4

A bacterium that uses light as an energy source and organic compounds as a carbon source is classified as a:

Accepted Answer

Photoheterotroph

Question 5

Which of the following is a chemical requirement for microbial growth that is a structural backbone of all organic molecules?

Accepted Answer

Carbon

Question 6

A scientist is culturing a fastidious bacterium that requires many growth factors. Which type of medium should she use?

Accepted Answer

Complex medium

Question 7

Which enzyme is responsible for removing superoxide radicals in bacteria?

Accepted Answer

Superoxide dismutase

Question 8

A hospital patient develops an infection associated with a catheter. Which microbial structure is most likely involved in the persistence of this infection?

Accepted Answer

Biofilm

Question 9

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 10

A microbiologist wants to preserve a bacterial culture for several years. Which method should she use?

Accepted Answer

Lyophilization

Question 11

Which of the following best explains why buffers are added to culture media?

Accepted Answer

To prevent changes in pH

Question 12

Which of the following statements about oxygen requirements is correct?

Accepted Answer

Facultative anaerobes can grow with or without oxygen

Question 13

A bacterial culture is growing in a medium with a pH of 5.5. Which group of organisms is most likely to thrive under these conditions?

Accepted Answer

Acidophiles

Question 14

Which of the following is a trace element required in small amounts and often functions as an enzyme cofactor?

Accepted Answer

Iron

Question 15

A scientist observes that a bacterial population doubles every 30 minutes. If she starts with 1,000 cells, how many cells will there be after 2 hours? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 1,000 	imes 2^4$ = 16,000$$

Question 16

Which of the following best describes the function of agar in culture media?

Accepted Answer

Acts as a solidifying agent

Question 17

Which toxic form of oxygen is the most reactive free radical?

Accepted Answer

Hydroxyl radical

Question 18

During which phase of the bacterial growth curve is there little or no increase in cell number as cells adjust to their environment?

Accepted Answer

Lag phase

Question 19

Which of the following best explains why biofilms are a concern in medical settings?

Accepted Answer

They are highly resistant to antimicrobial agents

Question 20

Which of the following statements about binary fission is correct?

Accepted Answer

It results in the number of cells doubling each generation

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

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