However, the citric acid cycle can not occur in the absence of oxygen because there is no way to regenerate the NAD+ used during this process. Lactic Acid Fermentation. The fermentation method used by animals and some bacteria like those in yogurt is lactic acid fermentation. This occurs routinely in mammalian red blood cells and in skeletal muscle that does not have enough oxygen.
During cellular respiration, glucose is broken down in the presence of oxygen to produce carbon dioxide and water. Energy released during the reaction is captured by the energy-carrying molecule ATP.