During respiration, most ATP is formed as a direct result of the net movement of which of the following across the inner mitochondrial membrane?

• A. Electrons through the citric acid cycle
• B. Protons (H\(^+\)) down their electrochemical gradient
• C. Oxygen into the mitochondrial matrix
• D. Glucose into the mitochondria

Answer: (B)

Verified step by step guidance

1. Understand the process of cellular respiration: Cellular respiration involves glycolysis, the citric acid cycle, and oxidative phosphorylation. ATP is primarily produced during oxidative phosphorylation, which occurs in the mitochondria.
2. Learn about the electron transport chain (ETC): The ETC is located in the inner mitochondrial membrane. Electrons are transferred through protein complexes, and this process drives the pumping of protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient.
3. Recognize the role of the proton gradient: The electrochemical gradient of protons (H⁺) across the inner mitochondrial membrane is essential for ATP synthesis. This gradient stores potential energy that is used to drive ATP production.
4. Understand chemiosmosis and ATP synthase: Protons (H⁺) flow back into the mitochondrial matrix through ATP synthase, a protein complex embedded in the inner mitochondrial membrane. This movement down their electrochemical gradient powers the synthesis of ATP from ADP and inorganic phosphate (Pi).
5. Identify the correct answer: The net movement of protons (H⁺) down their electrochemical gradient across the inner mitochondrial membrane is the direct result of ATP formation during oxidative phosphorylation.