Diagrams like food chains, food webs, and ecological pyramids help us understand how energy flows in ecosystems. All food chains, like the one below, start with primary producers. These organisms are autotrophs that get their energy directly from the sun through photosynthesis. The heterotrophs that follow must eat other organisms for energy. Primary consumers eat producers, secondary consumers eat primary consumers, and tertiary consumers, or apex predators, eat secondary consumers.

Each level of a food chain is called a trophic level. Each trophic level receives only 10% of the energy from the level below, with 90% lost as heat. This is called the 10% rule. For example, producers get 100% of their energy from the sun. Primary consumers get 10% of that energy, secondary consumers get 1%, and tertiary consumers get just 0.1%.

In this lab, you will simulate energy flow through an ecosystem to demonstrate the 10% rule.