The metabolic activity occurring in the living cells of all organisms in which complex organic compounds are broken down into simpler compounds with release of energy is called respiration. The process in which carbohydrates are completely oxidized into CO2 and H2O and energy are released in the form of ATP molecules, is called aerobic respiration. The process in which carbohydrates are incompletely oxidized without using into ethyl alcohol and CO2 is called anaerobic respiration.
