Final answer:
Only about 10% of energy is available for transfer to the next trophic level due to energy loss. The rest is used up or lost as heat or incompletely digested food.
Step-by-step explanation:
Energy is passed up a food chain or web from lower to higher trophic levels. However, generally only about 10 percent of the energy at one level is available to the next level. This is represented by the ecological pyramid. The remaining 90 percent of energy is used up at the lower trophic level or lost to the environment as heat or incompletely digested food.