Question

Match the correct stages of aerobic respiration to the given choices.

I. Maximum ATP production.
II. Carbon dioxide production.
III. Oxygen utilization.

• A. I- Chemiosmosis; II- Electron transport chain; III- Citric acid cycle
• B. I- Chemiosmosis; II- Citric acid cycle; III- Electron transport chain
• C. I- Citric acid cycle; II- Chemiosmosis; III- Electron transport chain
• D. I- Electron transport chain; II- Chemiosmosis; III- Citric acid cycle
• E. I- Electron transport chain; II- Citric acid cycle; III- Chemiosmosis

Answer 1

The correct option is B I- Chemiosmosis; II- Citric acid cycle; III- Electron transport chain

The citric acid cycle is the second phase of cellular respiration in which acetyl coA are enzymatically oxidized into carbon dioxide and the released energy is stored in NADH and FADH${}_2$. Electron transport chain includes downhill flow of electrons to a final electron acceptor (oxygen, which is then reduced into water) through a chain of membrane-bound carriers to facilitate the uphill transport of protons across a proton-impermeable membrane. Transfer of electrons through electron transport chain is accompanied by proton transfer across the membrane which in turn produces both a chemical gradient and an electrical gradient. Since inner mitochondrial membrane is impermeable to protons; protons can re-enter the matrix only through F${}_o$ particles of ATP synthase. The proton-motive force that drives protons back into the matrix provides the energy for ATP synthesis.

Therefore, the correct answer is option B.