Question 1

Which of the following best describes a psychrophile's cardinal temperature range?

Accepted Answer

Optimal growth at $$0\ ^\circ \mathrm{C} to$$ $$15\ ^\circ \mathrm{C}$$

Question 2

A food company wants to prevent microbial spoilage by adjusting the pH of its products. Which of the following best explains why lowering the pH can inhibit microbial growth?

Accepted Answer

Low pH denatures microbial enzymes, disrupting metabolism.

Question 3

Which statement correctly describes the movement of water in a bacterial cell placed in a hypertonic solution?

Accepted Answer

Water moves out of the cell, causing plasmolysis.

Question 4

Halophiles are microorganisms that:

Accepted Answer

Require high salt concentrations for growth.

Question 5

Which of the following is a primary function of carbon in bacterial cells?

Accepted Answer

Energy source and backbone for organic molecules.

Question 6

Nitrogen is essential for bacterial growth because it is used to:

Accepted Answer

Form the backbone of proteins and nucleic acids.

Question 7

Which enzyme is responsible for breaking down superoxide radicals ($$\mathrm{O}_2^-) in $$aerobic bacteria?

Accepted Answer

Superoxide dismutase

Question 8

A facultative anaerobe is grown in a test tube of nutrient broth. Where would you expect to see the most growth?

Accepted Answer

Throughout the tube, but more at the top

Question 9

Biofilms are medically significant because:

Accepted Answer

They increase antibiotic resistance and can form on medical devices.

Question 10

Which of the following best describes a chemically defined medium?

Accepted Answer

A medium where the exact chemical composition is known.

Question 11

A microbiologist wants to isolate a pure culture from a mixed sample. Which technique is most appropriate?

Accepted Answer

Streak plate method

Question 12

Which biosafety level (BSL) is appropriate for handling pathogens that pose a moderate risk and require lab coats, gloves, and eye protection?

Accepted Answer

BSL-2

Question 13

Which of the following is an indirect method for measuring bacterial growth?

Accepted Answer

Turbidity measurement using a spectrophotometer

Question 14

A bacterial culture is growing exponentially. If the initial population is $$N_0 = 100$ cells and the generation time is 30$ minutes, how many cells will there be after 2$ hours? (Assume no cell death.)

Accepted Answer

$$N = 100 	imes 2^4$ = 1600$$

Question 15

Which phase of bacterial growth is characterized by intense metabolic activity but no increase in cell number?

Accepted Answer

Lag phase

Question 16

Which of the following best describes the role of coenzymes in microbial metabolism?

Accepted Answer

They act as carriers for electrons or functional groups during enzymatic reactions.

Question 17

Agar is used in microbiological media because:

Accepted Answer

It is not metabolized by most bacteria and solidifies at room temperature.

Question 18

Which of the following is an example of selective media?

Accepted Answer

MacConkey agar, which inhibits Gram-positive bacteria.

Question 19

A bacterial cell is placed in a hypotonic solution. What is the most likely outcome?

Accepted Answer

Water enters the cell, possibly causing it to burst.

Question 20

Which method is best for preserving bacterial cultures for long-term storage?

Accepted Answer

Lyophilization (freeze-drying)

Microbial Growth: Environmental and Nutritional Requirements, Culture Methods, and Measurement

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