Energy is required by all organisms for their survival and this energy can be obtained from the food source. Only a group of organisms called autotrophs can prepare their own food, whereas all the consumers are dependent on the producers for the source of energy.
However when an organism obtains food by eating other organisms, it gets only a part of total energy. This means that only a part of total energy is transferred to the each level. This part accounts to only 10 percent of the total energy. This is because a lot of energy is wasted by an organism in carrying out the metabolic and cellular activities. Some of its portion is also wasted as heat and only remaining 10 percent is transferred to the next trophic level. If producers produced 1000 units of energy then the herbivores will receive only its 10 percent (100 units) and carnivores will receive 10 percent of the energy from herbivores (10 units).