Construct a food web from a list of organisms and calculate the energy available at each trophic level using the 10 percent rule.
Producers (plants, algae, some bacteria) capture energy from sunlight through photosynthesis and form the base of every food web. Primary consumers eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers; and decomposers (fungi and bacteria) break down dead material at every level, returning nutrients to the soil so producers can use them again. A food chain is one single path through this system; a food web is the more realistic tangle of many overlapping chains, since most organisms eat, and are eaten by, more than one thing.
Energy flow through this web follows last week's 10 percent rule: only about 10 percent of the energy at one trophic level typically transfers to the next, with the rest lost as heat. This is exactly why trophic pyramids narrow sharply toward the top, why food chains rarely have more than four or five links, and why top predators are naturally rare and need large territories to find enough food.
Mastery looks like: They can build a valid food web from a mixed list of organisms and correctly apply the 10% rule across two or more trophic transfers.
Common stumbles: Drawing a straight line instead of a branching web; forgetting decomposers, which closes the nutrient loop back to producers.