Which of the following processes produces the most ATP?

The electron transport chain is the process that produces the most ATP during cellular respiration. This step occurs in the inner mitochondrial membrane, where a series of protein complexes and other molecules work together to transfer electrons derived from NADH and FADH2, which are generated from earlier stages like glycolysis and the Krebs cycle.

As electrons move through the chain, they lose energy, which is used to pump protons (H+) across the mitochondrial membrane into the intermembrane space, creating an electrochemical gradient. This gradient represents potential energy, which drives protons back across the membrane through ATP synthase, a protein that synthesizes ATP from ADP and inorganic phosphate. The majority of ATP generated during cellular respiration—approximately 26 to 28 ATP molecules per glucose molecule—comes from this process.

In contrast, glycolysis and the Krebs cycle produce a smaller number of ATP directly. Glycolysis generates a total of 2 ATP molecules, and the Krebs cycle produces 2 ATP molecules for each glucose molecule processed, leading to a combined total of 4 ATP from these stages. Fermentation, while allowing ATP production in the absence of oxygen, generates only 2 ATP molecules per glucose molecule as it relies solely on glycolysis for energy. Therefore,