Oxygen accepts electrons at the end of the electron transport chain and combines with protons to form water, supporting usable cellular work and measurable biological activity.
Coverage 2016–2023 · Updated 15 Jul 2026
Chemiosmosis converts the proton gradient into ATP. The inner mitochondrial membrane restricts proton movement except through ATP synthase, so H⁺ diffuses from the intermembrane space back into the matrix through this enzyme. The flow drives phosphorylation of ADP to ATP; this is oxidative phosphorylation. At the end of the electron transport chain, oxygen accepts electrons and H⁺ to form water. Without oxygen, electron flow stops, the gradient collapses and oxidative ATP production cannot continue.
This objective is assessed through structured response, commonly using Identify / Describe.
Identify / Describe
Build the answer around this relationship: Oxygen is the final electron acceptor in the electron transport chain.
Representative question
Describe the role of oxygen in aerobic cell respiration.
In HL respiration, carbon and hydrogen are followed separately. Glycolysis turns glucose into pyruvate, net ATP, and reduced NAD. Without oxygen, pyruvate becomes lactate in humans or ethanol and carbon dioxide in yeast to regenerate NAD. With oxygen, pyruvate enters the link reaction, forming acetyl-CoA, carbon dioxide, and reduced NAD. The Krebs cycle releases more carbon dioxide and reduced coenzymes. Electron transport uses reduced NAD/FAD to pump protons, chemiosmosis through ATP synthase makes ATP, and oxygen accepts electrons and protons to form water. Substrate comparisons depend on ATP yield, oxygen demand, water production, and speed. Regenerated NAD allows glycolysis to continue. Fermentation regenerates NAD for glycolysis and is used in baking and brewing. Electron transfers release energy while coenzymes are reoxidized.
