Why does only about 10 percent of energy pass to the next trophic level?

When energy flows from one trophic level to the next, only about ten percent is stored and passed on, while roughly ninety percent is lost. This loss happens for several reasons. A large part of the energy is used up by the organism in its own life processes like respiration, movement and maintaining body temperature, and much of this leaves as heat. Some food is never eaten, some parts cannot be digested and are lost in faeces, and energy is also lost through excretion. Only the energy that becomes new body tissue, the growth of the organism, is available to the next level when it is eaten. Because so little passes on at each step, food chains are usually short, with only four or five levels, since there is not enough energy to support many more.