Trace the movement of matter through an ecosystem from producers through consumers and decomposers back to the environment, showing that matter cycles rather than disappearing.
Matter does not disappear in an ecosystem, it cycles. A producer pulls in matter, like carbon and water, from the air and soil to grow. A consumer eats the producer, and that matter becomes part of the consumer body. When any organism dies or releases waste, decomposers break that matter down into simple forms that return to the soil, water, and air, ready for a producer to use all over again.
This is the same conservation-of-matter idea from the matter unit, now happening on the scale of a whole ecosystem. Nothing that was part of a living thing truly vanishes; it just keeps moving through the cycle of growth, eating, death, and decay.
Mastery looks like: They can trace a piece of matter through producer, consumer, decomposer, and back to the environment, explaining that it cycles rather than disappears.
Common stumbles: Thinking decomposed matter is gone rather than returned to the soil in a usable form; missing the link back to conservation of matter.