Food Chains & Nutrient Cycling

Energy and nutrients are the lifeblood of every ecosystem. Understanding how energy flows through food chains and how nutrients are recycled is essential for the AQA GCSE Living World topic. This lesson explains food chains, food webs, trophic levels, and the nutrient cycle — and shows how these processes differ between biomes.

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Energy Flow in Ecosystems

All energy in an ecosystem ultimately comes from the Sun. Producers (green plants) capture solar energy through photosynthesis and convert it into chemical energy stored in glucose. This energy is then passed along the food chain when organisms eat each other.

The Basic Food Chain

A food chain shows the transfer of energy from one organism to the next in a linear sequence:

Sun → Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer

Example (UK woodland):

Sun → Oak tree (leaves) → Caterpillar → Blue tit → Sparrowhawk

The following diagram shows how energy flows through a typical ecosystem, including the role of decomposers in recycling nutrients: