Question 1

Which of the following best explains why microbial growth rate drops sharply above the optimum temperature?

Accepted Answer

Protein denaturation and collapse of the cytoplasmic membrane occur, leading to thermal lysis.

Question 2

A bacterium isolated from a hot spring grows optimally at $60^\circ C$. Which temperature class does it belong to?

Accepted Answer

Thermophile

Question 3

What is the primary reason that microbial growth cannot occur below the minimum temperature for a given species?

Accepted Answer

Membrane gelling prevents transport processes

Question 4

Which of the following equations represents the reaction catalyzed by catalase?

Accepted Answer

$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 5

A microorganism that can grow in the presence or absence of oxygen, but grows better with oxygen, is classified as which of the following?

Accepted Answer

Facultative anaerobe

Question 6

Which of the following best describes the growth of Escherichia coli with respect to temperature?

Accepted Answer

It is a mesophile, growing best at $39^\circ C$.

Question 7

Which of the following is a correct description of a hyperthermophile?

Accepted Answer

An organism that grows optimally at temperatures above $80^\circ C$.

Question 8

A culture of Thermococcus celer is incubated at $60^\circ C$ and $88^\circ C$. At which temperature would you expect maximal growth, and why?

Accepted Answer

$88^\circ C$, because Thermococcus celer is a hyperthermophile.

Question 9

Which of the following best explains why psychrotolerant organisms can survive in cold environments?

Accepted Answer

They possess membrane lipids that remain fluid at low temperatures.

Question 10

Which of the following reactions is catalyzed by superoxide dismutase?

Accepted Answer

$O_2^- + O_2^- + 2H^+ \rightarrow H_2O_2 + O_2$

Question 11

A bacterium isolated from an acid mine drainage site grows optimally at pH 2. Which adaptation is most likely present in its cellular machinery?

Accepted Answer

Membrane proteins resistant to proton influx.

Question 12

Which of the following best describes the relationship between temperature and enzymatic reaction rates in microorganisms?

Accepted Answer

Enzymatic rates increase with temperature up to an optimum, then decrease sharply due to denaturation.

Question 13

A facultative anaerobe is grown in a sealed jar with no oxygen. Which metabolic process will it most likely use?

Accepted Answer

Fermentation

Question 14

Which of the following is a likely consequence if a mesophilic bacterium is exposed to $80^\circ C$ for an extended period?

Accepted Answer

Protein denaturation and cell death

Question 15

Which of the following best describes the function of compatible solutes in osmophiles and xerophiles?

Accepted Answer

They balance osmotic pressure without interfering with cellular processes.

Question 16

A microorganism is found to pump inorganic ions into its cell in response to a hypertonic environment. What is the primary purpose of this adaptation?

Accepted Answer

To maintain turgor pressure and prevent plasmolysis.

Question 17

Which of the following best explains why some bacteria can survive in highly alkaline environments such as soda lakes?

Accepted Answer

They possess mechanisms to maintain internal pH near neutrality.

Question 18

Which of the following is a correct multi-step defense mechanism against reactive oxygen species in aerobic bacteria?

Accepted Answer

Superoxide dismutase converts $O_2^-$ to $H_2O_2$, then catalase converts $H_2O_2$ to $H_2O$ and $O_2$.

Microbial Growth and Environmental Control: Temperature and pH Effects

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