Explain how energy is transferred in a food web.

Sun to producers to herbivores to carnivores to decomposes etc.

Ecosystems are divided by trophic levels, which categorizes every organism by class of what kind of consumer they are. 90% of the energy that is available for an organism is lost as it is transferred through each trophic level. Producers, such as the plants of an ecosystem, have available 100% of the energy they can harvest and use 90% of it, thus leaving only 10% of energy left for primary consumers. Primary consumers then leave only 1% of that original energy for secondary consumers. Then secondary consumers leave only .01% of the initial energy for tertiary consumers. It is called the rule of 10% in biology and may be easier to comprehend as a list.
Producers energy total: 100%
Primary consumers energy total: 10%
Secondary consumers energy total: 1%
Tertiary consumers energy total: .01%
And so on...