Question 1

A food company wants to prevent the growth of spoilage bacteria in pickles by lowering the pH below 4.6. Which of the following best explains why this method is effective?

Accepted Answer

Most bacteria cannot grow at low pH because their enzymes denature and metabolic processes are disrupted.

Question 2

Which adaptation would you expect to find in the cell membrane of a hyperthermophilic archaeon living in a hot spring above 80°C?

Accepted Answer

A lipid monolayer with ether-linked lipids for increased thermal stability.

Question 3

A psychrophilic bacterium is isolated from Arctic sea ice. Which of the following features would most likely be found in its enzymes?

Accepted Answer

Flexible active sites that allow catalysis at low temperatures.

Question 4

Which of the following best describes the effect of high osmolarity (hypertonic environment) on a typical bacterial cell?

Accepted Answer

Water leaves the cell, causing plasmolysis and inhibition of growth.

Question 5

Which of the following is a key reason why Taq DNA polymerase from Thermus aquaticus is used in PCR?

Accepted Answer

It remains active at high temperatures required for DNA strand separation.

Question 6

A microbe that grows best at pH 9.5 and is commonly found in soda lakes is classified as a(n):

Accepted Answer

Alkaliphile

Question 7

Which of the following adaptations would you expect in a thermophilic microbe’s proteins?

Accepted Answer

Increased numbers of charged amino acids forming salt bridges for stability.

Question 8

A facultative anaerobe is introduced into a sealed jar with no oxygen. What will most likely happen to its growth rate compared to an oxygen-rich environment?

Accepted Answer

It will grow more slowly but still survive by switching to anaerobic metabolism.

Question 9

Which of the following best explains why lactic acid bacteria are used in yogurt production to prevent the growth of pathogens?

Accepted Answer

They ferment sugars to produce lactic acid, lowering the pH and inhibiting pathogens.

Question 10

Which of the following is a correct statement about the effect of temperature on microbial growth?

Accepted Answer

Growth rate increases with temperature up to an optimum, then rapidly declines as enzymes denature.

Question 11

A microbe isolated from a salt lake requires at least 10% NaCl for growth. Which term best describes this organism?

Accepted Answer

Halophile

Question 12

Which of the following is a mechanism by which acidification preserves food?

Accepted Answer

Organic acids enter microbial cells in undissociated form, dissociate inside, and acidify the cytoplasm.

Question 13

Which of the following best describes the function of chaperone proteins in thermophilic microbes?

Accepted Answer

They refold denatured proteins and prevent aggregation at high temperatures.

Question 14

A bacterium is exposed to a sudden increase in salt concentration. Which immediate cellular response is most likely?

Accepted Answer

Water leaves the cell, causing it to shrink and division proteins to cluster.

Question 15

Which of the following is a key adaptation of psychrophiles that allows them to maintain membrane fluidity at low temperatures?

Accepted Answer

High levels of polyunsaturated fatty acids in their membranes.

Question 16

Which of the following best explains why obligate anaerobes cannot survive in the presence of oxygen?

Accepted Answer

They lack enzymes to detoxify reactive oxygen species.

Question 17

Which of the following is a correct statement about the use of modified atmosphere packaging (MAP) in food preservation?

Accepted Answer

MAP reduces oxygen and increases carbon dioxide to inhibit aerobic spoilage microbes.

Question 18

Which of the following best describes the difference between sterilization and sanitization?

Accepted Answer

Sterilization kills all microbes, while sanitization reduces them to safe levels.

Question 19

A microbe is found to grow optimally at 37°C, is killed at 60°C, and cannot grow below 10°C. How would you classify this organism?

Accepted Answer

Mesophile

Question 20

Which of the following is a correct statement about the use of compatible solutes in microbial adaptation to osmotic stress?

Accepted Answer

Compatible solutes help retain water and maintain cell function in hypertonic environments.

lec 07:Environmental Limits on Microbial Growth: Temperature, pH, Osmolarity, and Oxygen

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