Sun is the ultimate source of the entire energy used by living things and, hence, it sustains the world of life. All the solar or light energy, however, does not reach the earth’s surface. Some of the solar energy reaching the earth’s surface is reflected back and lost as heat while some of it (only a fraction- about 0.1 percent of the total energy received from the sun by the earth) striking the green plants is fixed through photosynthesis. By the process of photosynthesis, the green plants make food from carbon dioxide and water with dissolved minerals in the presence of chlorophyll, using light energy and releasing oxygen. The absorbed light energy is, thus trapped as chemical energy which is then used by animals in the form of food.
When a plant is eaten by an animal, its organic substances get oxidized liberating energy. Some of the liberated energy is used up in the synthesis of cellular constituents of the animal and build up its tissues and the rest is lost as heat. When a second animal eats the first, the organic substances of the first animal get oxidized releasing energy. Again whole of the liberated energy is not used up for synthesizing cellular constituents of the animal (here, second animal) but some of it is lost as heat. Ultimately, whole of the energy intially entrapped by the plants during photosynthesis is changed into heat and lost and all the carbon of the organic substances is oxidized to carbon dioxide.
a flow or transfer of energy from the sun to the plants, from the plants to the plant-eating animals (herbivorous), from the plant-eating animals to the flesh-eating animals (carnivorous) and finally to decomposers. The decomposers act on dead or decaying plants or animals and make available their constituents to the plants.
a fall in useful energy at every successive level of nutrition, because some of it is lost as heat at each transformation of energy.