The electron transport chain is a series of reactions in the cristae where hydrogen is oxidised to water and 34 ATP are produced. This is indicative of which metabolic pathway?

• A. Glycolysis
• B. Krebs cycle
• C. Electron transport chain
• D. Anaerobic glycolysis

Answer: (C)

Oxidative phosphorylation is the stage of aerobic respiration where the energy from electrons is used to pump protons across the inner mitochondrial membrane (cristae) and drive ATP synthesis. In the electron transport chain, electrons are passed along a series of carriers and ultimately reduce oxygen to water. The proton gradient created powers ATP synthase to convert ADP and Pi into ATP, yielding a large amount of ATP per glucose—about 30–34 in many cells. The description fits this stage precisely: hydrogen is oxidised to water and a substantial amount of ATP is produced.

Glycolysis happens in the cytoplasm and yields only a small amount of ATP and does not produce water at this stage. The Krebs cycle generates reduced cofactors and a smaller direct ATP yield, but most ATP comes from the electron transport chain. Anaerobic glycolysis occurs without oxygen and results in lactate or ethanol formation, with little ATP produced compared to aerobic respiration.