Which part of cellular respiration produces the most ATP?

The process of cellular respiration is essential for the production of ATP, the energy currency of the cell. The electron transport chain is where the majority of ATP is generated. This system, located in the inner mitochondrial membrane, utilizes high-energy electrons derived from NADH and FADH2, which are produced during glycolysis and the Krebs cycle. As the electrons are passed through a series of protein complexes in the chain, they release energy that is used to pump protons (H+) across the mitochondrial membrane, creating a proton gradient.

This gradient generates potential energy, akin to water stored behind a dam. The protons flow back across the membrane through a protein complex called ATP synthase, which harnesses this flow to synthesize ATP from ADP and inorganic phosphate. This mechanism is highly efficient, producing the vast majority of ATP molecules during cellular respiration—approximately 28 to 32 ATPs per glucose molecule, depending on the organism and conditions.

In contrast, the Krebs cycle and glycolysis each produce only a limited amount of ATP—specifically 2 ATP molecules from glycolysis and 2 ATP molecules from the Krebs cycle per glucose molecule directly. Fermentation, which occurs in the absence of oxygen, produces even less ATP. Therefore, while all