Here's why:
* Cellular Respiration: Glycolysis, the first stage of cellular respiration, breaks down glucose into two molecules of pyruvate. This pyruvate then moves on to the subsequent stages (Krebs cycle and electron transport chain) to generate ATP.
* Fermentation: Fermentation also starts with glycolysis, producing pyruvate. However, instead of proceeding to the Krebs cycle and electron transport chain, pyruvate is converted into other products (like lactate in lactic acid fermentation or ethanol in alcoholic fermentation). This happens because fermentation occurs in the absence of oxygen, which is needed for those later stages.
So, while the final products differ significantly between cellular respiration and fermentation, both processes begin with the breakdown of glucose to pyruvate.
