Question 1

Which of the following best describes the overall redox reaction for methanogenesis from carbon dioxide and hydrogen?

Accepted Answer

$$\mathrm{CO_2$ + 4H_2 \rightarrow CH_4$ + 2H_2O}$$

Question 2

Methanogenesis from acetate involves which of the following reactions?

Accepted Answer

$$\mathrm{CH_3COOH \rightarrow CH_4$ + CO_2$}$$

Question 3

Which of the following statements best explains the difference between respiration and fermentation?

Accepted Answer

Respiration uses an external electron acceptor, while fermentation uses an internal organic molecule as the electron acceptor.

Question 4

During the oxidation of methane by methanotrophs, which intermediate is directly incorporated into biomass via the serine pathway?

Accepted Answer

Formaldehyde ($$\mathrm{CH_2O})$$

Question 5

Which of the following best describes how redox balance is achieved during fermentation?

Accepted Answer

By transferring electrons from NADH to organic intermediates, regenerating NAD$$^+.$$

Question 6

Which of the following is a key difference between homo-fermentation and mixed acid fermentation?

Accepted Answer

Homo-fermentation produces primarily one end product, while mixed acid fermentation produces several acids and alcohols.

Question 7

Clostridia are known for fermenting sugars anaerobically. Which of the following is a typical end product of Clostridial fermentation?

Accepted Answer

Butyric acid

Question 8

In a syntrophic relationship between ethanol fermenters and methanogens, what is the primary benefit for the ethanol fermenter?

Accepted Answer

Removal of hydrogen, making ethanol fermentation energetically favorable.

Question 9

Which of the following best describes the aerobic oxidation of aromatic hydrocarbons?

Accepted Answer

Involves incorporation of oxygen into the aromatic ring, leading to ring cleavage.

Question 10

Anaerobic oxidation of aliphatic hydrocarbons typically involves which of the following electron acceptors?

Accepted Answer

Sulfate ($$\mathrm{SO_4$^{2-}})$$

Question 11

A bioreactor is inoculated with a methanogen and supplied with methylamine ($$\mathrm{CH_3NH_2}) as $$the sole carbon source. Which of the following best describes the expected metabolic process?

Accepted Answer

Methanogenesis from methyl compounds, producing methane and ammonia.

Question 12

Which of the following equations represents the oxidation of methane under aerobic conditions?

Accepted Answer

$$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$

Question 13

Which of the following best explains why fermentation yields less ATP than respiration?

Accepted Answer

Fermentation does not use an electron transport chain or oxidative phosphorylation.

Question 14

A culture of bacteria is fermenting glucose and producing a mixture of lactic acid, ethanol, and acetic acid. Which type of fermentation is this?

Accepted Answer

Mixed acid fermentation

Question 15

Which of the following is a common misconception about syntrophy?

Accepted Answer

Syntrophy requires direct physical contact between the two organisms.

Question 16

Which of the following best describes the fate of electrons in fermentation?

Accepted Answer

They are transferred to organic molecules, forming reduced end products.

Question 17

Which of the following is a key step in the anaerobic oxidation of aromatic hydrocarbons?

Accepted Answer

Addition of fumarate to the aromatic ring to initiate degradation.

Question 18

A wastewater treatment plant relies on methanogenesis to reduce organic load. If hydrogen accumulates in the system, what is the most likely consequence?

Accepted Answer

Methanogenesis will slow down due to unfavorable energetics.

Question 19

Which of the following best describes the role of methanotrophs in the global carbon cycle?

Accepted Answer

They oxidize methane to carbon dioxide, reducing greenhouse gas emissions.

Question 20

Which of the following is a distinguishing feature of hydrocarbon metabolism under aerobic versus anaerobic conditions?

Accepted Answer

Aerobic metabolism uses oxygenases to activate hydrocarbons, while anaerobic metabolism uses addition reactions such as fumarate addition.

Metabolic Diversity II: Carbon Metabolism in Microorganisms

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