Final answer:
As energy moves up the food chain, about 90% of the energy is lost, primarily through metabolic heat and other biological processes, leading to typically no more than four trophic levels in an ecosystem.
Step-by-step explanation:
When energy is transferred up a food chain or food web, there is a significant loss at each step. Approximately 90 percent of the energy at one trophic level is not transferred to the next level. This energy is instead used by organisms for metabolism, growth, and repair, which generates heat—a form of energy that is lost to the environment.
In addition, some energy is also lost through excretion of incompletely digested food. Due to this energy loss, ecosystems rarely sustain more than four trophic levels, with a fifth being an exception rather than the rule.