Using a food chain from a grassland, show its trophic levels. Explain why the energy reaching the top carnivore is far less than the energy trapped by the grass, and why it never flows back.

1. 1 · Define. A food chain is a series of organisms through which food energy passes, as each eats the one below it.
2. 2 · Give an example. Grass → grasshopper → frog → snake → hawk, at trophic levels I to V.
3. 3 · Explain one-way flow. Energy moves from the sun to plants to consumers; it never flows back to an earlier level.
4. 4 · Explain the loss. At each step most energy is used for moving, digesting and breathing, or is lost as heat.
5. 5 · Draw it. [Food chain with arrows from food to eater, and the energy getting smaller at each level]
6. 6 · Close in one line. So energy flow is unidirectional and food chains stay short.

Scoring tip: Point every arrow from the food to the eater, and label each trophic level.