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Types of Respiration
Depending on the availability and non-availability of free oxygen, respiration is of two types:
a) Aerobic respiration
b) Anaerobic respiration
a) Aerobic respiration:
Aerobic respiration takes places when there is abundance of free atmospheric oxygen. It results in the complete oxidation of stored food such as sugar and carbohydrates into water and carbon dioxide with the liberation of large amount of heat and energy. Aerobic respiration is more efficient than anaerobic respiration due to complete oxidation. This process occurs in all living cells and especially takes places place inside the mitochondria of living cells. Aerobic respiration is summarized by the following chemical reactions:
The above chemical reaction shows only the starting and end of a very complicated process involving more than fifty different reactions, each catalyzed by different enzyme.
b) Anaerobic respiration :
Microorganisms such as yeast and certain bacteria obtain most of their energy by a form of anaerobic respiration, called fermentation. Typical product of fermentation is alcohol. Many types of yeast are used in alcoholic fermentation. The chemical equation is given below:
C6H12O6 = 2C2H5OH + 2CO2 + 210 KJ of energy
Green plants can respire anaerobically for only short period as alcohol is toxic to the tissue in high concentration.
In higher animals, during heavy exercise, breathing rate and heart beat increases but there is a limit to the speed at which they can delivery oxygen to muscles and this, in turn limits the speed at which aerobic respiration can supply energy to muscles. However, muscles can respire without oxygen anaerobically for a short time.
During short exercise, when oxygen supplies are no longer sufficient to meet energy demands, the rate of anaerobic respiration increases rapidly in the muscles, but this type of respiration produces lactic acid instead of carbon dioxide and water.
Lactic acid accumulates in muscle eventually preventing further contraction. This lactic acid is broken down into carbon-dioxide and water and energy aerobically. This is noticed in the breathlessness of athletes after races.
Thus, anaerobic and aerobic respiration are closely linked and infact, majority of organisms perform both anaerobic and aerobic reaction.