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The first law of thermodynamics states that energy can neither be created or destroyed, but can be converted from one form to another.

  1. Solar energy obtained from sun is the only source of energy for all the living organisms on earth.
  2. This solar energy is converted into chemical energy by plants through the process of photosynthesis.
  3. This energy captured by autotrophs does not go back into the solar system but passes from the autotrophs (green plants) to herbivores who feed on green plants. 
  4. Producers capture only 1-5% of the photosynthetically active radiation (PAR) and remaining unutilized energy is released in the form of heat.
  5. A small portion of the energy captured is utilized by the producers for their respiration and only about 10% energy is used to provide food to the herbivores.
  6. Energy obtained by the herbivores is used in metabolism and the utilized portion is added to the detritus as faeces and liberated in the form of heat.
  7. The remaining portion of energy in the herbivores is utilized by carnivores or transferred to the decomposers when the herbivores die.
  8. In this step also, only about 10% of energy in herbivore is used by the carnivore.
  9. Thus, at every trophic level there is decreased in the amount of energy available for organisms of the next trophic level.
  10. This proves the second law of thermodynamics which states that energy is lost at every step in the ecosystem in the form of heat.
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