Q: A student is asked to calculate the standard free energy change ($$\Delta G^\circ') $$for a redox reaction with $$n = 2$$ electrons transferred and $$\Delta E^\circ' = +0.15 V. $$What is the correct calculation? (Faraday's constant $$F = 96,485 J/V$$·mol)

$$\Delta G^\circ' = -2 \times 96,485 \times 0.15 = -28,945.5 J/$$mol

Question 1

Which of the following best describes the difference between catabolism and anabolism in microbial metabolism?

Accepted Answer

Catabolism breaks down complex molecules to release energy, while anabolism uses energy to build complex molecules from simpler ones.

Question 2

A bacterium is fermenting glucose to lactic acid. Which of the following statements about the process is correct?

Accepted Answer

Fermentation generates ATP primarily through substrate-level phosphorylation.

Question 3

Which of the following equations correctly represents the calculation of free energy change ($$\Delta G) $$for a redox reaction?

Accepted Answer

$$\Delta G = -nF\Delta E^\circ'$$

Question 4

During aerobic respiration in prokaryotes, what is the primary role of the electron transport chain?

Accepted Answer

To transfer electrons from NADH and FADH$$_2 to $$oxygen, generating a proton gradient across the membrane.

Question 5

Which of the following best explains how NAD$$^+/$$NADH cycling supports microbial metabolism?

Accepted Answer

NADH donates electrons to the electron transport chain, regenerating NAD$$^+$$ for continued glycolysis.

Question 6

A student is asked to calculate the standard free energy change ($$\Delta G^\circ') $$for a redox reaction with $$n = 2$$ electrons transferred and $$\Delta E^\circ' = +0.15 V. $$What is the correct calculation? (Faraday's constant $$F = 96,485 J/V$$·mol)

Accepted Answer

$$\Delta G^\circ' = -2 	imes 96,485 	imes 0.15 = -28,945.5 J/$$mol

Question 7

Which of the following statements correctly compares fermentation and aerobic respiration?

Accepted Answer

Aerobic respiration uses an electron transport chain, while fermentation does not.

Question 8

In the context of microbial metabolism, what is the main function of the proton motive force (PMF)?

Accepted Answer

To drive the synthesis of ATP via ATP synthase.

Question 9

A facultative anaerobe is growing in the absence of oxygen but in the presence of nitrate. Which metabolic process is most likely being used for energy generation?

Accepted Answer

Anaerobic respiration

Question 10

Which of the following best describes the role of electron carriers such as cytochromes and quinones in the electron transport chain?

Accepted Answer

They transfer electrons between complexes, facilitating the generation of a proton gradient.

Question 11

A mutation in a bacterium prevents the regeneration of NAD$$^+$$ from NADH. What is the most likely consequence for glycolysis?

Accepted Answer

Glycolysis will slow down or stop due to a lack of available NAD$$^+.$$

Question 12

Which of the following is a key difference between anaerobic respiration and fermentation in prokaryotes?

Accepted Answer

Anaerobic respiration uses an electron transport chain with a non-oxygen terminal electron acceptor, while fermentation does not use an electron transport chain.

Question 13

A microbe is using sulfate ($$\mathrm{SO}_4$$^{2-}$$) as a terminal electron acceptor. Which process is this microbe performing?

Accepted Answer

Anaerobic respiration

Question 14

Which of the following statements about redox reactions in microbial metabolism is correct?

Accepted Answer

The substance that is oxidized loses electrons, and the substance that is reduced gains electrons.

Question 15

In a clinical scenario, a patient’s wound is infected with a bacterium that can only survive in the absence of oxygen and produces ethanol and CO$$_2 as $$metabolic end products. Which metabolic pathway is most likely being used by this bacterium?

Accepted Answer

Fermentation

Question 16

Which of the following best explains why fermentation is necessary for some microbes in the absence of an external electron acceptor?

Accepted Answer

Fermentation regenerates NAD$$^+$$ from NADH, allowing glycolysis to continue.

Question 17

A researcher measures the reduction potential ($$E^\circ') of $$two half-reactions: A/B = $$-0.32 V $$and C/D = $$+0.22 V. If $$electrons flow from A/B to C/D, what is the standard free energy change ($$\Delta G^\circ') $$for the transfer of 2 electrons? (Use $$F = 96,485 J/V$$·mol)

Accepted Answer

$$\Delta G^\circ' = -2 	imes 96,485 	imes (0.22 - (-0.32)) = -2 	imes 96,485 	imes 0.54 = -104,603.4 J/$$mol

Question 18

Which of the following is a real-world example of a microbe using anaerobic respiration?

Accepted Answer

Escherichia coli using nitrate ($$\mathrm{NO}_3^-) as a $$terminal electron acceptor in the human gut.

Question 19

Which of the following best describes how ATP synthase uses the proton motive force (PMF) to generate ATP?

Accepted Answer

Protons flow down their electrochemical gradient through ATP synthase, driving the phosphorylation of ADP to ATP.

Question 20

A bacterium is exposed to a chemical that dissipates the proton gradient across its membrane. What is the most likely effect on ATP production?

Accepted Answer

ATP production by ATP synthase will decrease significantly.

Microbial Metabolism: Fundamentals, Electron Transfer, Fermentation, and Respiration

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