RESPIRATION

The organisms require energy of perform their normal activities. This energy is obtained by metabolizing the food that they eat. Green plants prepare their own food from carbon dioxide and water in the presence of sunlight by a process called photosynthesis. Whereas animals eat the already prepared food.

        How do the digested food provide energy? The products of digestion viz glucose, amino acid and fatty acids etc. contain chemical energy in them. When these compounds are metabolized and degraded,  a large amount of energy is usually released. For example, a molecule of glucose on complete oxidation releases 686,000 calories.

         The energy is utilized in carrying out the normal activities of organism, as for example, contraction of muscles which brings about movement and breathing of heart etc. mostly a single activity requires considerably less energy for its accomplishment, than is released from a complete oxidation of a glucose, protein and fatty acid molecule. The nature has, therefore, devised a system in which the chemical energy of glucose, protein and fatty acid on degradation
(catabolism) is trapped into small packets of energy in the form of ATP molecules. A molecule of ATP on its breakdown release only 7300 calories of energy. Many ATP molecules, as required for a particular activity, can be available to provided the energy needed. This is the most economical arrangement of nature.

           The oxidation of the absorbed food material in order to obtain energy is called respiration.

            There are two methods of respiration in the organism.

      Some organism oxidize ;their food without using any molecular oxygen. This is known as anaerobic respiration. In this type of respiration considerably less amount of energy is produced as compared with the other type of respiration.

      In anaerobic respiration  a glucose molecule is broken down into two molecules of lactic acid with a release of only 47,000 calories of energy.

      In most of the higher and larger organisms, the glucose is oxidized by using molecular oxygen. This type of respiration is known as aerobicrespiration. In aerobic respiration a mole of glucose is oxidized completely into carbon dioxide and water releasing enormous amount of energy . one glucose molecule in this respiration produces 686,000 calories of energy. Aerobic respiration thus produces 20 times more energy than anaerobic respiration.