Only 10% of the energy is passed on to each trophic level of an energy pyramid. This is because most of the energy available at any trophic level is used by an organism in internal bodily activities like cell respiration, ATP production, several life processes, metabolism etc. Thus, even though a large amount of energy is taken at a trophic level, nearly 90% of it is used by the organism itself and thus only 10% of the total energy is available for passing onto the next level. This is the reason why organism at the apex of an energy pyramid receives the least energy.
