Respiration is the physiological process in which complete and incomplete oxidation of organic food takes place. In respiration, the oxidation of various organic food substances like carbohydrates may take place. The process of respiration occurs in all living cells of plants and animals and generally called cellular respiration. The energy produced during the process is used in all the life activities of the organisms. It is a catabolic process that occurs in mitochondria and cytoplasm of the cell and represented by the following chemical equation.
C6H12O6 + 6O2 -> 6CO2 + H2O + Energy (2868 Kcal or 686 Kcal)
The main facts associated with respiration are:
- Consumption of atmospheric oxygen
- Release of energy by break down of organic food.
- Liberation of carbon dioxide and a small quantity of water.
- Oxidation and decomposition of reserve food.
Types of respiration: Based on the availability of oxygen during the process, respiration can be classified into two types.
- Aerobic respiration: Respiration which occurs in the presence of oxygen and organic food material is completely oxidized into CO2 and H2O with the release of energy called aerobic respiration.
+ Energy (2868 Kcal or 686 Kcal)
- Anaerobic respiration: This respiration which occurs in the absence of oxygen and the organic food material is incompletely oxidized into ethyl alcohol and CO2 with a little amount of energy is called anaerobic respiration. It occurs in the cytoplasm of a cell. Such type of respiration generally occurs in lower organisms like bacteria and fungi. It also occurs in many tissues of higher plants, seed in storage, fleshy fruits, and muscles of animals. This process of incomplete oxidation is known as fermentation in the case of bacteria and fungi.
C6H12O6 → CO2 + C2H5OH + 50 kcal
Krebs’s Cycle (TCA – Cycle)
It occurs inside the mitochondrial matrix of the inner chamber. Its details were given by Sir Hans Krebs in 1948. It is also called the citric cycle (because the first stable product is citric acid) or Tricarboxylic Acid (because citric acid contains three 3-COOH groups). Krebs’s Cycle is completed in eight successive steps.