Here's why:

* Glycolysis: This initial stage of respiration produces a small amount of ATP (2 molecules per glucose).

* Krebs Cycle (Citric Acid Cycle): This cycle produces some ATP (2 molecules per glucose), but its primary role is to generate electron carriers (NADH and FADH2).

* Electron Transport Chain: This final stage utilizes the high-energy electrons from NADH and FADH2 to power a proton gradient across the mitochondrial membrane. This gradient is then used to drive ATP synthesis by ATP synthase, generating the majority of ATP (around 32-34 molecules per glucose).

Therefore, the electron transport chain is the most significant contributor to ATP production during aerobic respiration.