Flow of energy through various trophic l | Class 12 Biology Chapter Ecosystem, Ecosystem NCERT Solutions

An ecosystem does not have its own source of energy so they receive the energy from the sun. Incoming solar radiations trapped by the producers (green plants) and change this energy into the chemical energy in the synthesis of food. When the green plants are eaten by the herbivores with the efficiency of energy capture 1% of sunlight, a lot of energy amount is lost as heat or consumed in the metabolic reactions for their growth and the rest is used for the development or reproduction. When the primary consumers ate the herbivores 10% (10% law) of the amount of energy of herbivores is transferred to the primary consumers level and so on. Thus when the energy is transferred at each level, less amount of usable energy is available for the last trophic level. Flow of energy is always unidirectional and shows upright pyramid because energy captured by the producers or the green plants does not revert back to the solar input but it passes to the herbivores for their metabolic reactions. And, when the energy is passed to the herbivores it does not go back to the producers but passes to the primary consumers or the carnivores. At each trophic level there would be a progressive decrease in the energy due to the energy is lost as heat in respiration, development and reproduction. Let us take an example: consider the use of energy by the herbivores (primary consumers). Herbivores ingest some plant biomass and produces faeces and this faecal matter energy will not pass along to the primary carnivore. The chemical energy of the food is assimilated by the herbivores i.e. liberated by the cellular respiration is used for the tissue repair , body movements and other functions and which is turned as heat and will not pass along to the primary carnivore. Some ingested chemical energy from the herbivore is converted into the biomass and can be served as food for the primary carnivore. Some herbivores can be directly eaten by the carnivores. Much of the chemical energy present in the herbivores do not transfer to carnivores. So as a result energy get diminished by following the 10% law from one trophic level to the preceding level over the same period of time. Essentially all of the energy captured by photosynthesis in an ecosystem eventually becomes heat as the chemical energy is used by various trophic levels.