Questions: Energy stored in a proton gradient is used to synthesize ATP from ADP and P during what process in oxidative phosphorylation? Glycolysis Fermentation Chemiosmosis Citric acid cycle

The answer is the third one (Chemiosmosis): Energy stored in a proton gradient is used to synthesize ATP from ADP and $\mathrm{P}_{\mathrm{P}}$ during what process in oxidative phosphorylation?

Explanation for each option:

1. Glycolysis: Incorrect. Glycolysis is the process of breaking down glucose into pyruvate, producing a small amount of ATP and NADH. It does not involve the synthesis of ATP from a proton gradient.
2. Fermentation: Incorrect. Fermentation is an anaerobic process that allows glycolysis to continue by regenerating NAD+ from NADH. It does not involve the use of a proton gradient to synthesize ATP.
3. Chemiosmosis: Correct. Chemiosmosis is the process by which the energy stored in a proton gradient across a membrane is used to drive the synthesis of ATP from ADP and inorganic phosphate (Pi) via ATP synthase during oxidative phosphorylation.
4. Citric acid cycle: Incorrect. The citric acid cycle (Krebs cycle) is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA. It produces NADH and FADH2 but does not directly involve the synthesis of ATP from a proton gradient.

Summary: The correct answer is Chemiosmosis, as it directly involves the use of a proton gradient to synthesize ATP during oxidative phosphorylation.