Aerobic cellular respiration uses oxygen to break down glucose molecules into adenosine triphosphate (ATP). The inputs into cellular respiration are oxygen and glucose, while the outputs are carbon dioxide, water and ATP.
Breakdown of glucose through aerobic cellular respiration produces a lot of energy for the amount of glucose that goes in if there is oxygen. One glucose molecule produces 36 ATP molecules. By contrast, anaerobic lactic acid fermentation does not require oxygen but only produces two ATP molecules. Lactic acid fermentation is responsible for making muscles feel tired during vigorous exercise. Yeast exclusively uses anaerobic respiration to break down glucose and creates alcohol as a byproduct.