THE ROLE OF OXYGEN IN RESPIRATION AND THE PATHWAYS
OF ELECTRON FLOW IN THE ABSENCE OF OXYGEN
Questions
1. What is the role of oxygen in aerobic respiration?
o A) It is used to produce glucose.
o B) It acts as the final electron acceptor in the electron transport chain.
o C) It is used to generate NADH.
o D) It is used to convert pyruvate to acetyl-CoA.
2. What is formed when oxygen accepts electrons and combines with protons in
aerobic respiration?
o A) Carbon dioxide
o B) Water
o C) Glucose
o D) ATP
3. What would happen if oxygen was not available in the electron transport chain?
o A) The Krebs cycle would stop.
o B) NADH and FADH2 would accumulate.
o C) Oxygen would be substituted by another molecule.
o D) All of the above
4. In the absence of oxygen, which of the following pathways is primarily used to
regenerate NAD+?
o A) The electron transport chain
o B) The citric acid cycle
o C) Fermentation
o D) Glycolysis
5. Which type of fermentation occurs in human cells during oxygen debt (e.g.,
during intense exercise)?
o A) Alcoholic fermentation
o B) Lactic acid fermentation
o C) Acetyl-CoA fermentation
o D) Glucose fermentation
6. What is the final electron acceptor in fermentation pathways?
o A) Oxygen
o B) NAD+
o C) Pyruvate or Acetaldehyde
o D) FADH2
7. What is produced in alcoholic fermentation in yeast?
o A) Lactic acid
o B) Oxygen
o C) Ethanol and carbon dioxide
o D) Glucose and oxygen
8. During lactic acid fermentation, which molecule is reduced to form lactic acid?
o A) NADH
o B) NAD+
o C) Pyruvate
o D) Acetyl-CoA
9. How does the absence of oxygen affect the electron transport chain (ETC)?
o A) The ETC continues to function normally, but at a slower rate.
o B) The ETC stops, and NADH cannot be oxidized.
o C) Oxygen becomes the final electron donor in the chain.
o D) The ETC shifts to glycolysis.
10. What is the effect of a lack of oxygen on ATP production?
o A) ATP production decreases because the electron transport chain is not
active.
o B) ATP production increases due to fermentation.
o C) ATP production remains the same due to glycolysis.
o D) ATP production stops completely.
11. Which process allows cells to continue producing ATP in the absence of oxygen?
o A) The electron transport chain
o B) Glycolysis
o C) Krebs cycle
o D) Chemiosmosis
12. What is the main purpose of fermentation?
o A) To produce ATP in the absence of oxygen
o B) To produce glucose from lactic acid
o C) To generate oxygen for cellular respiration
o D) To generate carbon dioxide and water
13. Which of the following describes the process of lactic acid fermentation?
o A) NADH is oxidized to NAD+ by pyruvate, forming lactic acid.
o B) Pyruvate is converted to ethanol and carbon dioxide.
o C) NADH is reduced to form ethanol.
o D) NAD+ is produced by the electron transport chain.
14. Which molecule is the primary electron carrier in the absence of oxygen?
o A) Oxygen
o B) NADH
o C) Acetyl-CoA
o D) FADH2
15. Which of the following is true regarding electron flow in the absence of oxygen?
o A) The electron transport chain can operate normally without oxygen.
o B) Electrons from NADH are transferred to the electron transport chain and
ATP is produced.
o C) NADH must be oxidized to NAD+ through fermentation pathways.
o D) Oxygen is still used in the electron transport chain.
Answer Key
1. B) It acts as the final electron acceptor in the electron transport chain.
2. B) Water
3. B) NADH and FADH2 would accumulate.
4. C) Fermentation
5. B) Lactic acid fermentation
6. C) Pyruvate or Acetaldehyde
7. C) Ethanol and carbon dioxide
8. A) NADH
9. B) The ETC stops, and NADH cannot be oxidized.
10. A) ATP production decreases because the electron transport chain is not active.
11. B) Glycolysis
12. A) To produce ATP in the absence of oxygen
13. A) NADH is oxidized to NAD+ by pyruvate, forming lactic acid.
14. B) NADH
15. C) NADH must be oxidized to NAD+ through fermentation pathways.