Here's why:
* Glycolysis: This initial stage breaks down glucose into pyruvate, producing a small amount of ATP (2 molecules) and NADH.
* Krebs Cycle (Citric Acid Cycle): This cycle further breaks down pyruvate, generating some ATP (2 molecules), NADH, and FADH2.
* Electron Transport Chain: This is where the majority of ATP is produced. The NADH and FADH2 generated in the previous stages deliver electrons to the electron transport chain. As these electrons move down the chain, a proton gradient is created across the mitochondrial membrane. The flow of protons back across the membrane drives ATP synthesis, generating a large amount of ATP (around 34 molecules).
Therefore, while glycolysis and the Krebs cycle are important for preparing molecules for the electron transport chain, the electron transport chain is responsible for the vast majority of ATP produced during aerobic respiration.
