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?