The percent of energy that passes on from one trophic level to the next is typically around 10%. This is known as the 10% rule.

Here's why this happens:

* Energy loss in metabolic processes: Organisms use a significant portion of the energy they consume for their own metabolic processes, such as growth, movement, and maintaining body temperature. This energy is lost as heat.

* Incomplete digestion: Not all of the food an organism consumes is digested and absorbed. Some of it is passed out as waste.

* Predation: Only a portion of the organisms at one trophic level are consumed by predators at the next level.

This means that only about 10% of the energy from one trophic level is available to the next. This is why food chains typically have only 4-5 trophic levels; there isn't enough energy to sustain more.

It's important to note that the 10% rule is a general guideline, and the actual percentage can vary depending on several factors, including:

* The type of ecosystem

* The specific organisms involved

* The efficiency of energy transfer in different species

However, the 10% rule provides a useful framework for understanding the flow of energy through ecosystems and the limitations on the number of trophic levels.