Question 1

Which of the following best describes the role of carbon in microbial life?

Accepted Answer

Carbon is required for the synthesis of proteins, lipids, nucleic acids, and carbohydrates.

Question 2

A bacterium isolated from a glacier is found to grow optimally at 10°C, but can survive at 0°C. Which temperature class does it belong to?

Accepted Answer

Psychrophile

Question 3

Which equation correctly calculates the generation time ($$g) $$for a microbial population?

Accepted Answer

$$g = \frac{t}{n}$$

Question 4

What is the main difference between defined and complex media?

Accepted Answer

Defined media have an exact known chemical composition, while complex media contain digests of biological materials with unknown composition.

Question 5

Which phase of the bacterial growth curve is characterized by zero net increase in cell number due to nutrient depletion or waste accumulation?

Accepted Answer

Stationary phase

Question 6

A sample contains $$1.5 	imes 10^7$ cells/mL as determined by a Petroff-Hausser counting chamber. What is the main limitation of this method?

Accepted Answer

It cannot distinguish between living and dead cells.

Question 7

Which of the following is true about Mannitol Salt Agar (MSA)?

Accepted Answer

It is both selective and differential, selecting for halotolerant bacteria and differentiating based on mannitol fermentation.

Question 8

Which process allows certain bacteria to convert atmospheric nitrogen ($$N_2) $$into ammonia ($$NH_3$$)?

Accepted Answer

Nitrogen fixation

Question 9

Which of the following best explains why oxygen is toxic to some microorganisms?

Accepted Answer

Oxygen produces reactive byproducts such as superoxide anion ($$O_2$$^-$$), hydrogen peroxide (H_2O_2$), and hydroxyl radical (OH$$^-$$).

Question 10

Which type of microorganism would most likely be found in a salt lake with $$a_w = 0.75$$?

Accepted Answer

Extreme halophile

Question 11

Which laboratory technique is used to obtain a pure culture of a single microbe from a mixed sample?

Accepted Answer

Streak plate technique

Question 12

Which of the following statements about biofilms is correct?

Accepted Answer

Biofilms are communities of cells enmeshed in a polysaccharide matrix attached to a surface.

Question 13

Which of the following is a correct description of the decimal reduction time ($$D) in $$heat sterilization?

Accepted Answer

$$D is $$the time required at a given temperature to reduce the viability of a microbial population to 10%.

Question 14

Which of the following is NOT a function of magnesium (Mg) in microbial cells?

Accepted Answer

Serving as a terminal electron acceptor in respiration

Question 15

Which type of medium would you use to distinguish between bacteria that can ferment lactose and those that cannot?

Accepted Answer

Differential medium

Question 16

A bacterium grows best at pH 9. Which physiological class does it belong to?

Accepted Answer

Alkaliphile

Question 17

Which of the following is a correct application of the spread-plate method?

Accepted Answer

Counting only surface colonies

Question 18

Which of the following statements about autoclaving is true?

Accepted Answer

The high temperature (121°C) kills the microbes, including endospores.

Question 19

Which chemical agent is classified as a sterilant and is used for temperature-sensitive materials such as plastics?

Accepted Answer

Ethylene oxide (gas)

Question 20

Which adaptation allows psychrophilic microorganisms to maintain membrane fluidity at low temperatures?

Accepted Answer

Higher unsaturated and shorter-chain fatty acid content

Microbial Growth and Its Control – Comprehensive Study Notes

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