The biochemical process during which energy is released in stages as chemical bonds are broken in steps is called respiration. This process takes place in the mitochondria of the cell of most of the living organisms. Respiration that takes place in the mitochondria of the cell in the presence of oxygen is called aerobic respiration.

The process of respiration that occurs in the absence of oxygen in higher plants is anaerobic respiration. The anaerobic and incomplete breakdown of glucose that results in a gain of two ATP and alcohol and CO2 is known as alcoholic fermentation. Microorganisms like yeast exhibit this process when placed in sugar solution. Foaming results takes place during this process.