During aerobic glycolysis, NADH produced by oxidation of glyceraldehyde-3-phosphate, is oxidized by the mitochondrial electron transport chain, with the electrons transferred ultimately to oxygen. This oxidation of NADH, considered in detail in Chapter 15 (see here), yields additional energy, with about 3 moles of ATP synthesized from ADP per mole of NADH oxidized. Since 2 moles of NADH are produced per mole of glucose entering the pathway, aerobic glycolysis yields considerably more ATP than anaerobic glycolysis.

In anaerobic glycolysis, electrons from NADH do not enter the electron transport chain (see here). Anaerobic glycolysis pathways include lactate fermentation and ethanol fermentation.

Metabolism of glucose to either lactate or ethanol represents a nonoxidative process, as you can see by comparing the empirical formulas for glucose (C6H12O6) and lactate (C3H6O3). Clearly, there is no change in the overall oxidation state of the carbons, because the numbers of hydrogens and oxygens bound per carbon atom are identical for glucose and lactate. The same is true for ethanol plus CO2, when one counts the atoms in both. However, some individual carbon atoms of lactate and ethanol plus CO2 undergo oxidation, and some become reduced.