Why respiration provides cells with more energy per molecule of glucose than does fermentation?
In respiration, glycolysis occurs which is the breakdown of glucose into 2 molecules of pyruvate, in the process, yielding 2 molecules of ATP per glucose. Under aerobic conditions, the presence of oxygen allows pyruvate to be completely oxidized, yielding about 36 molecules of ATP per glucose. Due to the absence of oxygen in anaerobic respiration, link reaction, Krebs cycle and oxidative phosphorylation cannot take place. Pyruvate is converted to ethanol in plants and yeast or lactate in mammals to regenerate NAD+ which is needed for glycolysis. Glucose is incompletely oxidized in anaerobic respiration and a lot of energy is trapped in ethanol or lactate, thus yielding only 2 molecules of ATP per glucose from glycolysis.
