What are the two pathways that might follow glycolysis?

Cellular respiration and fermentation are two pathways that follow glycolysis. Cellular respiration requires oxygen, while fermentation occurs in its absence. Cellular respiration consists of a chemical pathway named the Krebs cycle or the citric acid cycle, followed by an electron transport system.

A transition reaction occurs after glycolysis and before either respiration or fermentation begins. Pyruvate, the product of glycolysis, is processed into acetyl-CoA, a high-energy molecule. Krebs-cycle reactions process the acetyl-CoA into electron-carrying molecules ATP and NADH. The electron transport system passes those through chemical gradient membranes to create additional ATP used to power cellular processes. Fermentation converts acetyl-CoA into ethanol or lactic acid.