In ecosystems, useful energy flows in a one-way path. It enters the living things from the physical world, passes from one organism to a different and eventually escapes back to the physical environment in a less useful form. Energy enters an ecosystem from the Sun. Solar radiations are absorbed by the Earth’s surface through the atmosphere. The process of photosynthesis is carried out by these radiations. Also, they help to maintain the Earth’s temperature for the survival of living organisms. Few of the solar radiations are reflected by the Earth’s surface. However, a very little 2-10 percent of solar energy is captured by green plants (producers) during photosynthesis to be converted into food. The total rate of photosynthesis, including the organic matter that is almost immediately used up in plant respiration, is termed as ‘gross primary productivity. When these green plants are consumed by herbivores, only 10% of the stored energy from producers is transferred to herbivores. For various processes such as respiration, growth, and reproduction, the remaining 90% of the energy is used. Similarly, only 10% of the energy of herbivores is transferred to carnivores. Therefore, this is called the ten percent law of energy flow.