How do cellular respiration and fermentation depend on glycolysis?

The processes that help our bodies turn the calories we eat into ATP (chemical energy) are called cellular respiration and fermentation. The first step in both processes is glycolysis. If your body has enough oxygen, cellular respiration takes place and you produce a lot of ATP; if not, fermentation occurs and your body produces a lot less ATP.

Both cellular respiration and fermentation depend on glycolysis as the initial step in the breakdown of glucose to produce energy. During glycolysis, glucose is converted into two molecules of pyruvate, along with the production of ATP and NADH. In cellular respiration, pyruvate enters the citric acid cycle (Krebs cycle) to generate more ATP through oxidative phosphorylation. This process requires oxygen and occurs in the presence of aerobic conditions. In contrast, during fermentation, pyruvate is converted into either lactic acid or ethanol and carbon dioxide, depending on the organism and type of fermentation. Fermentation allows for the regeneration of NAD+ from NADH, which is essential for sustaining glycolysis in the absence of oxygen. Therefore, both cellular respiration and fermentation rely on glycolysis to generate the initial substrates needed for energy production.