Key Idea: Topic 2.4 explains how energy enters ecosystems (producers), how it moves through trophic levels (consumers), why food chains link into food webs, and how decomposers recycle nutrients to keep ecosystems running.
🌿 Producers (start of every food chain)
Without producers, no consumers can survive — they are the energy foundation.
🦊 Consumers and feeding types
🔗 Food chains and trophic levels
Exam rule: arrows in food chains show the direction of energy transfer, not “who eats who”.
🕸️ Food webs (real ecosystems)
♻️ Decomposers and nutrient recycling
High marks: link both ideas — energy flow (one-way) AND nutrient cycling (recycled by decomposers).
1) Define producer vs consumer. 2) What’s a trophic level? 3) What do arrows show? 4) Food chain vs food web? 5) Detritivores vs saprotrophs?