MCAT Biology : Anaerobic Metabolic Pathways

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Anaerobic Metabolic Pathways

What is the purpose of the formation of lactic acid during anaerobic respiration?

Possible Answers:

It allows FAD to reform

It allows NADH to reform

It allows FADH2 to reform

It allows glucose to reform

It allows NAD+ to reform

Correct answer:

It allows NAD+ to reform

Explanation:

Cells need a constant supply of NAD+ to accept electrons during glycolysis in order to produce pyruvate from glucose.

Example Question #2 : Anaerobic Metabolic Pathways

Which statement is FALSE when comparing aerobic to anaerobic respiration?

Possible Answers:

Aerobic respiration creates more ATP from each glucose molecule used.

Both processes produce pyruvate.

Aerobic repsiration is responsible for the muscle pain felt during strenuous exercise.

Both processes begin with glycolysis.

Correct answer:

Aerobic repsiration is responsible for the muscle pain felt during strenuous exercise.

Explanation:

Anaerobic respiration creates the byproduct lactic acid. Accumulation of lactic acid in the muscles due to lack of oxygen results in the pain we experience during exercise. Remember that aerobic respiration creates 36 ATP molecules per glucose, while anaerobic repiration forms only 2 ATP molecules per glucose. Since both processes begin with glycolysis, pyruvate is still generated.

Note that while lactic acid is responsible for the "burn" in muscles during exercise, other agents are responsible for muscle soreness after exercise.

Example Question #3 : Anaerobic Metabolic Pathways

While running a marathon, an individual feels pain and a burning sensation in her legs. One reason for this is the conversion of pyruvate into lactic acid which the body does in order to __________.

Possible Answers:

regenerate FADH from FADH2

regenerate NADfrom NADH

regenerate NADH from NAD+

regenerate FADH2 from FADH

Correct answer:

regenerate NADfrom NADH

Explanation:

In the absence of available oxygen, the body conducts metabolism anaerobically in a process known as fermentation. During strenuous exercise, like running a marathon, the body needs to generate ATP at a rate faster than oxygen is becoming available.

To combat this issue, the body converts pyruvate and NADH, generated in glycolysis, into lactic acid and NAD+, respectively. This regenerated NADcan participate in further glycolysis to generate more ATP, even in the absence of oxygen. Oxygen only becomes a necessary reactant in the electron transport chain; thus, glycolysis can continue to generate limited amounts of ATP in an anaerobic environment as long as NAD+ is present.

Example Question #3 : Anaerobic Metabolic Pathways

Which choice accurately states the amount of ATP produced from a single glucose molecule in an anaerobic environment and in an aerobic environment, respectively?

Possible Answers:

Anaerobic respiration produces 2 ATP; aerobic respiration produces 36 ATP

Anaerobic respiration produces 34 ATP; aerobic respiration produces 2

Anaerobic respiration produces 40 ATP; aerobic respiration produces 4 ATP

Anaerobic respiration produces 4 ATP; aerobic respiration produces 8 ATP

Anaerobic respiration produces 2 ATP; aerobic respiration produces 2 ATP

Correct answer:

Anaerobic respiration produces 2 ATP; aerobic respiration produces 36 ATP

Explanation:

In an anaerobic environment, two net ATP are produced from glycolysis. Since glycolysis requires an investment of two ATP and produces four ATP, it has a total net yield of two ATP. In an aerobic environment, however, the cell performs glycolysis, pyruvate decarboxylation, the citric acid cycle, and oxidative phosphorylation. These processes together yield a net of 36 ATP.

Example Question #4 : Anaerobic Metabolic Pathways

What is the purpose of fermentation?

Possible Answers:

To generate ATP

To produce disaccharides

To oxidize pyruvate

To generate NAD+

To generate carbon dioxide

Correct answer:

To generate NAD+

Explanation:

Fermentation occurs in the absence of oxygen, and reduces pyruvate to the end product of either ethanol or lactic acid. Since pyruvate is being reduced, NADH is oxidized to NAD+, which is needed for the initial glycolysis reaction to produce pyruvate. During anaerobic respiration, glycolysis is still able to function, but only if NAD+ is available; thus, fermentation allows the regeneration of NAD+ in order for glycolysis to proceed in the absence of oxygen.

Example Question #5 : Anaerobic Metabolic Pathways

Which of the following products cannot be directly formed from pyruvate?

Possible Answers:

Acetyl-CoA

Acetaldeyde

None of these can be formed from pyruvate

Ethanol

Lactic acid

Correct answer:

Ethanol

Explanation:

Pyruvate can be decarboxylated to make acetyl-CoA. This is the process that initiates the citric acid cycle. Pyruvate can also undergo fermentation, and be reduced to either lactic acid or acetaldehyde. Acetaldehyde can then be reduced to ethanol, however, pyruvate cannot directly be converted to ethanol.

Example Question #6 : Anaerobic Metabolic Pathways

Which process can occur under anaerobic conditions?

Possible Answers:

Pyruvate dehydrogenase complex (PDC)

Glycolysis

Oxidative phosphorylation

Kreb's cycle

Electron transport chain

Correct answer:

Glycolysis

Explanation:

Glycolysis occurs in the cytosol and does not require oxygen. The pyruvate dehydrogenase complex (PDC) and Kreb's cycle require oxygen indirectly, while the electron transport chain and oxydative phosphorylation require oxygen directly. After glycolysis produces pyruvate, either aerobic respiration or anaerobic respiration can proceed depending on the availability of oxygen.

Example Question #7 : Anaerobic Metabolic Pathways

How many molecules of ATP would be produced and available for use if four molecules of glucose were used during anaerobic respiration?

Possible Answers:

8

12

20

16

Correct answer:

8

Explanation:

Two net molecules of ATP are produced via anaerobic cellular respiration.

Example Question #8 : Anaerobic Metabolic Pathways

What is the net ATP production if 4 glucose molecules are oxidized in anaerobic conditions?

Possible Answers:

Correct answer:

Explanation:

During anaerobic conditions only glycolysis occurs. Glycolysis alone produces 4 ATP per glucose, but requires an input of 2 ATP per glucose. Thus, 2 ATP per glucose are yielded through glycolysis.

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