1. In the absence of oxygen, the pyruvate formed during glycolysis (the break down of glucose) can’t be used to make more ATP; thus, glycolysis is the only source of ATP for cellular functions since glycolysis is the only source of ATP. it must be kept going.
2. NAD occurs in many living cells and functions as an electron acceptor. Oxidation is loss of electrons and reduction is gain of electrons. NAD is used alternately with NADH in metabolic reactions to gain or lose electrons. Glycolysis reduces NAD+ to NADH + H+, depleting the supply of NAD and without NAD+, glycolysis will come to a halt. Therefore, NADH + H+ must be oxidized back to NAD+. Fermentation allows for the oxidation of NADH + H+ back to NAD+, by reducing pyruvate to either lactate (in animals lactic acid causes sore muscles) or ethanol (yeast produce alcohol when fermenting beer or wine and give off CO2).
Anaerobic respiration in animals:
Anaerobic respiration in yeast:
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