Which process yields ATP via the electron transport chain and chemiosmotic coupling?

• A. Glycolysis
• B. Krebs cycle
• C. Oxidative phosphorylation
• D. Fermentation

Answer: (C)

The process that yields ATP via the electron transport chain and chemiosmotic coupling is oxidative phosphorylation. In this step, electrons are transferred through a series of protein complexes in the inner mitochondrial membrane (the electron transport chain). As electrons move, protons are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient. ATP synthase then uses this proton motive force to drive the synthesis of ATP from ADP and inorganic phosphate. Oxygen acts as the final electron acceptor, allowing the chain to continue; without it, the chain stalls and oxidative phosphorylation stops.

Glycolysis and the Krebs cycle each produce reducing equivalents (NADH/FADH2) that feed into the electron transport chain, but their own ATP production largely occurs through substrate-level phosphorylation, not via chemiosmotic coupling. Fermentation, on the other hand, operates without the electron transport chain and relies on substrate-level phosphorylation to generate a small amount of ATP while regenerating NAD+.