What is the major difference between cellular respiration and fermentation?

The major difference between cellular respiration and fermentation lies in the role of the electron transport chain and the oxidation of NADH. In cellular respiration, after glycolysis, the NADH produced is oxidized in the electron transport chain, which is a series of reactions that occurs in the mitochondria. This process allows cells to harness the energy stored in electrons, ultimately producing a significant amount of ATP through oxidative phosphorylation.

In contrast, fermentation occurs in the absence of oxygen and does not utilize the electron transport chain. Instead, it primarily relies on substrate-level phosphorylation to generate ATP and involves the regeneration of NAD+ from NADH without the production of ATP via the electron transport chain. This results in a lower yield of ATP compared to cellular respiration.

Understanding this distinction helps clarify why the oxidation of NADH in the electron transport chain is essential for the high ATP output associated with cellular respiration, showcasing its efficiency compared to fermentation.