Final answer:
Energy is lost primarily as heat during metabolic processes at each trophic level due to the second law of thermodynamics, and only about 10% of energy is passed to the next level in a food chain.
Step-by-step explanation:
Most of the energy contained in one trophic level is lost when it gets to the next trophic level. The lost energy takes the form of heat due to metabolic processes, and through excretion of undigested food. In an ecological context, this concept is explained by the second law of thermodynamics, which dictates that energy conversions are inefficient, leading to a loss of usable energy and an increase in disorder or entropy within the system. As energy moves up the food chain, each trophic level retains only about 10% of the energy from the level below, which is illustrated by the ecological energy pyramid.
As organisms use energy for growth, metabolism, and repair, most of it is expended in these processes. The result is that after a limited number of transfers between trophic levels, there is insufficient energy left to sustain a large population at a higher trophic level, which is why most food chains contain only a few levels.