4. Fermentation

It is the process of production of organic acid or alcohol through the reduction of pyruvate produced by glycolysis of sugar (glucose). It occurs in the anaerobic respiration process. It is a substrate-level phosphorylation process where 2 ATP molecules are produced from a single glucose molecule. The end product is either lactic acid or ethanol. These products can’t enter oxidative phosphorylation due to a lack of oxygen. Hence no further ATP molecules are produced. Therefore, it is less effective than the aerobic respiration process in ATP generation.