Apply the law of conservation of matter and the first and second laws of thermodynamics to explain why matter cycles through ecosystems while energy flows through in one direction.
Matter is never created or destroyed, only rearranged -- the law of conservation of matter. This has a blunt environmental consequence: there is no "away." When you throw something out, burn it, or flush it, its atoms do not vanish; they move to the air, the water, the soil, or a landfill and change form. Understanding pollution starts with tracking where matter actually goes.
Energy behaves differently. The first law of thermodynamics says energy cannot be created or destroyed either, only converted from one form to another (sunlight into chemical energy in a leaf, for instance). But the second law adds a catch: every energy conversion loses some usable energy as low-grade heat. That is why energy cannot be recycled the way aluminum can -- once it has degraded to heat and spread out, it cannot be gathered back up to do useful work again. This is the deep reason ecosystems need a constant new supply of sunlight, while their chemical elements (carbon, nitrogen, water) can be reused indefinitely.
Mastery looks like: They can explain, using their own example, why matter cycles but energy flows one-way through a system, and apply the 10% rule correctly across two or more trophic transfers.
Common stumbles: Thinking energy simply "disappears" rather than converting to less useful heat; treating "away" as an actual destination rather than just another part of the same planet.