Which stage of cellular respiration directly produces the most ATP?

The electron transport chain is the stage of cellular respiration that directly produces the most ATP. This process takes place in the inner mitochondrial membrane, where the transfer of electrons through a series of protein complexes generates a proton gradient across the membrane. As protons flow back into the mitochondrial matrix through ATP synthase—an enzyme that utilizes this gradient—ATP is synthesized from ADP and inorganic phosphate.

This mechanism, known as oxidative phosphorylation, harnesses the energy derived from the high-energy electrons produced during previous stages of cellular respiration, namely glycolysis and the Krebs cycle. While glycolysis and the Krebs cycle contribute to the overall ATP yield, they generate significantly fewer molecules of ATP directly compared to the vast amount produced during the electron transport chain. Fermentation, on the other hand, does not produce ATP through this mechanism and is generally less efficient in energy yield, primarily functioning in anaerobic conditions. Thus, the electron transport chain is unequivocally the most prolific stage for ATP production.