Q: Which equation best represents the process of plasmolysis in a bacterial cell placed in a hypertonic solution?

$$\text{Plasmolysis:} \, [\text{NaCl}]_{\text{medium}} \u003e [\text{NaCl}]_{\text{cell}} \rightarrow \text{Water leaves cell}$$

Question 1

Which group of microorganisms is most likely to cause spoilage in refrigerated foods, and why?

Accepted Answer

Psychrotrophs, because they grow between $$0^{\circ}C$ and 20$$^{\circ}$$C to$$ $$30^{\circ}C$.

Question 2

Why are hyperthermophiles that grow at temperatures above $$100^{\circ}C$ seemingly limited to oceanic depths?

Accepted Answer

Because oceanic depths provide high pressure, preventing water from boiling at $$100^{\circ}C$.

Question 3

A bacterial culture is growing in a medium with a pH of 4.5. Which type of microorganism is most likely to thrive in this environment?

Accepted Answer

Acidophiles

Question 4

What is the primary reason for controlling the pH of culture media when growing bacteria?

Accepted Answer

To ensure optimal enzyme activity and prevent denaturation.

Question 5

Which equation best represents the process of plasmolysis in a bacterial cell placed in a hypertonic solution?

Accepted Answer

$$	ext{Plasmolysis:} \, [	ext{NaCl}]_{	ext{medium}} \u003e [	ext{NaCl}]_{	ext{cell}} ightarrow 	ext{Water leaves cell}$$

Question 6

Why might primitive civilizations have used food preservation techniques that rely on osmotic pressure?

Accepted Answer

To inhibit microbial growth by causing plasmolysis in bacteria.

Question 7

Which element is primarily used as the structural backbone of organic molecules in microbial cells?

Accepted Answer

Carbon

Question 8

If bacterial cells were given a sulfur source containing radioactive sulfur ($$^{35}S) in $$their culture media, in which molecules would the $$^{35}S be $$found?

Accepted Answer

Amino acids, thiamine, and biotin

Question 9

Which of the following best describes the oxygen requirements of microaerophiles?

Accepted Answer

Require oxygen concentration lower than air.

Question 10

How do aerobes avoid damage by toxic forms of oxygen?

Accepted Answer

By producing enzymes such as superoxide dismutase and catalase.

Question 11

Which of the following is a plausible explanation for why Bacillus cereus multiplies more rapidly in deep containers of rice compared to shallow containers?

Accepted Answer

Deep containers cool more slowly, keeping rice in the danger zone longer.

Question 12

Which of the following is NOT a chemical requirement for microbial growth?

Accepted Answer

Osmotic pressure

Question 13

A microbe is found growing only at the bottom of a test tube of solid growth medium. Which oxygen classification does it most likely belong to?

Accepted Answer

Obligate anaerobe

Question 14

Which of the following trace elements is most likely required as an enzyme cofactor in microbial metabolism?

Accepted Answer

Iron

Question 15

Which equation best represents the conversion of superoxide radicals to less toxic forms in aerobic bacteria?

Accepted Answer

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

Question 16

Which of the following best describes the role of biofilms in infection?

Accepted Answer

Biofilms increase resistance to microbicides and shelter pathogens from environmental factors.

Question 17

Which of the following is a real-world example of a biofilm causing a medical problem?

Accepted Answer

Biofilm formation on catheters leading to persistent infections.

Question 18

Which organic growth factor must microbes obtain from their environment because they cannot synthesize it themselves?

Accepted Answer

Vitamins

Question 19

A microbe is able to grow in both the presence and absence of oxygen, but grows best when oxygen is available. Which classification does it belong to?

Accepted Answer

Facultative anaerobe

Question 20

Which of the following best explains why molds and yeasts can grow at lower pH values than most bacteria?

Accepted Answer

Their enzymes are adapted to function in acidic environments.

Microbial Growth: Physical and Chemical Requirements, Oxygen Effects, and Biofilms

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