Question 1

Which of the following statements best explains why fermentation is necessary for cells that lack a respiratory chain?

Accepted Answer

Fermentation enables the regeneration of NAD+ from NADH, permitting glycolysis to continue.

Question 2

During alcoholic fermentation by Saccharomyces, what is the net ATP yield per glucose molecule, and which enzyme is responsible for converting acetaldehyde to ethanol?

Accepted Answer

Net ATP yield is $$2$$, and the enzyme is alcohol dehydrogenase.

Question 3

Which of the following best describes substrate-level phosphorylation?

Accepted Answer

ATP is synthesized by transferring a phosphate group from an organic substrate directly to ADP.

Question 4

A facultative anaerobe is growing in an environment with both oxygen and nitrate available. Which pathway will it preferentially use and why?

Accepted Answer

It will use aerobic respiration because oxygen yields the highest ATP per glucose.

Question 5

In homolactic fermentation, what is the fate of pyruvate and how many carbons are present in the waste product?

Accepted Answer

Pyruvate is converted to lactate; the waste product has $$3$$ carbons.

Question 6

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

Accepted Answer

Fermentation regenerates NAD+ without an electron transport chain, while respiration uses an electron transport chain to regenerate NAD+.

Question 7

A protozoan such as Trichomonas lacks mitochondria and chloroplasts. Which organelle does it use for ATP production, and what is the main pathway?

Accepted Answer

It uses hydrogenosomes and produces ATP via fermentative pathways.

Question 8

Which of the following electron carriers is NOT a protein?

Accepted Answer

Quinone

Question 9

In the citric acid cycle, acetyl-CoA (2 carbons) combines with oxaloacetate (4 carbons) to form citrate. What is the total number of carbons in citrate?

Accepted Answer

$$6$$

Question 10

How many NADH molecules are produced per glucose molecule during glycolysis, the intermediate step, and the citric acid cycle combined?

Accepted Answer

$$10$$

Question 11

Which of the following best describes the role of ATP synthase in cellular respiration?

Accepted Answer

It catalyzes the reaction $$\mathrm{ADP} + \mathrm{P_i} \rightarrow \mathrm{ATP}$$ using energy from proton flow.

Question 12

Which pathway produces the greatest net ATP per glucose molecule?

Accepted Answer

Aerobic respiration

Question 13

In heterolactic fermentation, how many net ATP are produced per glucose molecule, and what are the main waste products?

Accepted Answer

Net ATP is $$1$$; waste products are lactate, ethanol, and CO$$_2.$$

Question 14

Which of the following statements about the electron transport chain is correct?

Accepted Answer

Electrons are transferred from carrier to carrier, and protons are pushed outside the membrane, creating a proton gradient.

Question 15

Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA in the intermediate step between glycolysis and the citric acid cycle?

Accepted Answer

Pyruvate dehydrogenase complex

Question 16

If a cell removes alpha-ketoglutarate from the citric acid cycle for biosynthesis, which alternative pathway can replenish oxaloacetate?

Accepted Answer

Glyoxylate cycle

Question 17

Which of the following is true regarding anaerobic respiration?

Accepted Answer

It uses a terminal electron acceptor other than oxygen, such as nitrate or sulfate.

Question 18

What is the main purpose of fermentation in microbial metabolism?

Accepted Answer

To regenerate NAD+ so glycolysis can continue.

Question 19

Which of the following statements about the proton motive force is correct?

Accepted Answer

It is generated by the movement of protons across a membrane during electron transport.

Question 20

In aerobic respiration, how many ATP are produced per glucose molecule, accounting for substrate-level and oxidative phosphorylation?

Accepted Answer

$$38$$

Fermentation and Respiration: Microbial Metabolic Pathways

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