Food Chains and Food Webs

This lesson covers food chains, food webs, energy transfer and pyramids of biomass as required by the Edexcel GCSE Combined Science specification (1SC0). You need to construct and interpret food chains and webs, understand energy flow through trophic levels and explain the shape of biomass pyramids.

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Food Chains

A food chain shows the flow of energy from one organism to the next in a single pathway. Each organism feeds on the one before it.

Example:

grass → rabbit → fox → eagle

• Grass = producer (trophic level 1)
• Rabbit = primary consumer (trophic level 2)
• Fox = secondary consumer (trophic level 3)
• Eagle = tertiary consumer (trophic level 4)

The arrows in a food chain show the direction of energy transfer — they always point from the organism being eaten to the organism doing the eating.

Exam Tip: The arrow means "is eaten by" or "energy flows to". Never draw the arrows backwards.

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Food Webs

In reality, most organisms eat more than one type of food. A food web shows the interconnected food chains within an ecosystem.