Question 1

Which of the following best describes the function of magnesium (Mg) in microbial cells?

Accepted Answer

Stabilizes ribosomes, membranes, and nucleic acids; also required by many enzymes

Question 2

A microbiologist is culturing a marine microbe that requires sodium (Na) for growth. Which type of culture medium would be most appropriate?

Accepted Answer

Defined medium containing NaCl and other essential salts

Question 3

Which equation correctly relates the initial cell number ($N_0$) and the cell number at time $t$ ($N$) during exponential growth, given $n$ generations?

Accepted Answer

$N = N_0 	imes 2^n$

Question 4

A batch culture of bacteria is observed to have a lag phase after inoculation. What is the primary reason for this lag phase?

Accepted Answer

Cells are altering their metabolic state and synthesizing new enzymes

Question 5

Which of the following is a limitation of direct microscopic cell counts using a counting chamber?

Accepted Answer

Cannot distinguish between live and dead cells without additional stains

Question 6

A spectrophotometer is used to measure the optical density (OD) of a bacterial culture. What is the relationship between OD and cell number for unicellular organisms?

Accepted Answer

OD is proportional to cell number within certain limits

Question 7

Which of the following best explains the 'great plate count anomaly' in environmental microbiology?

Accepted Answer

Direct microscopic counts reveal more organisms than plate counts due to diverse growth requirements

Question 8

In a chemostat, which parameter is used to control the specific growth rate ($k$) of the microbial culture?

Accepted Answer

Dilution rate ($D = F/V$)

Question 9

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

Accepted Answer

Higher unsaturated and shorter-chain fatty acid content

Question 10

A microorganism isolated from a soda lake grows optimally at pH 9. Which physiological class does it belong to?

Accepted Answer

Alkaliphile

Question 11

Which of the following is a compatible solute commonly used by halophilic bacteria to maintain positive water balance?

Accepted Answer

Glycine betaine

Question 12

Which enzyme is responsible for converting superoxide anion ($O_2^-$) to hydrogen peroxide ($H_2O_2$) in aerobic microorganisms?

Accepted Answer

Superoxide dismutase

Question 13

Which physical method is most effective for sterilizing heat-sensitive liquids in the laboratory?

Accepted Answer

Filtration using membrane filters

Question 14

A bacteriostatic agent is added to a bacterial culture. What is the expected effect?

Accepted Answer

Cell growth is inhibited, but cells are not killed

Question 15

Which of the following best describes the function of an autoclave in microbial control?

Accepted Answer

Uses steam under pressure to achieve high temperatures and kill endospores

Question 16

Which microbial growth phase is characterized by zero population growth due to nutrient depletion or waste accumulation?

Accepted Answer

Stationary phase

Question 17

Which equation represents the dilution rate ($D$) in a chemostat, where $F$ is the flow rate and $V$ is the culture volume?

Accepted Answer

$D = F / V$

Question 18

Which of the following is a real-world consequence of exponential microbial growth, as seen in food spoilage?

Accepted Answer

Cell numbers increase rapidly, leading to spoilage (e.g., lactic acid bacteria in milk)

Question 19

Which antimicrobial agent is nontoxic enough to be applied to living tissues and is used as a topical antiseptic?

Accepted Answer

Antiseptic (e.g., 60–85% ethanol)

Question 20

A microbiologist wants to determine the minimum inhibitory concentration (MIC) of a new antibiotic. Which method would be most appropriate?

Accepted Answer

Serial dilution in liquid medium followed by observation of growth inhibition

Chapter 4

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