Which process is responsible for producing the majority of ATP during aerobic respiration?

During aerobic respiration, the majority of ATP is produced through the electron transport chain. This process occurs in the inner mitochondrial membrane and involves a series of protein complexes and electron carriers that transfer electrons derived from NADH and FADH2, which are generated during glycolysis and the Krebs cycle. As electrons move through these complexes, energy is released, which is used to pump protons (H+) across the membrane, creating a proton gradient.

Once the protons accumulate in the intermembrane space, they flow back into the mitochondrial matrix through ATP synthase, a process known as chemiosmosis. The flow of protons drives the synthesis of ATP from ADP and inorganic phosphate (Pi). This step is highly efficient, producing the largest number of ATP molecules compared to glycolysis and the Krebs cycle, which generate only a limited amount of ATP directly.

Moreover, fermentation is not a part of aerobic respiration, but rather an anaerobic process that occurs in the absence of oxygen, leading to significantly less ATP production. By contrast, glycolysis and the Krebs cycle serve mainly to produce electron carriers that feed into the electron transport chain, helping to facilitate the high yield of ATP during aerobic respiration.