Some metabolites can be converted to amino acids by transamination, transfer of an amino acid group to an organic acid. Anaerobic bacteria produce lactic acid when we manufacture some cheeses. Yeasts use CO 2 to make bread rise, produce alcohol in winemaking. Animals reduce pyruvate to lactate when it is produced faster than it can be oxidized by Krebs cycle. Despite low yield of two ATP molecules, fermentation provides quick burst of ATP energy for muscular activity.
Disadvantage is that lactate is toxic to cells.
Individual is in oxygen debt because oxygen is still needed after exercising. Two ATP produced per glucose molecule during fermentation is equivalent to 14.6 kcal. 2 O during cellular respiration results in 686 kcal. of energy.