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Every food chain starts with a producer: a plant, algae or phytoplankton that makes its own food, usually by photosynthesis.

Primary consumers (herbivores) eat producers. Secondary consumers eat herbivores, and tertiary consumers eat secondary consumers. An apex predator at the top has no predators. Example: grass → grasshopper → rat → snake → hawk.

Each food chain is just one path that food and energy can take. In an ecosystem many food chains overlap and link up: together they make a food web.

Experiment: The food web string game

1. Give each pupil a card and stand in a circle. Pupils with producers stand together.
2. The teacher starts with grass. Pass the wool from the grass to an animal that eats grass; keep hold of your part of the wool.
3. Keep passing the wool from food to eater until every card is connected (some cards will hold several strands).
4. Now the 'rabbit' gently pulls its strand. Who feels it? These are the living things that would be affected if rabbits disappeared.
5. Energy maths: if the grass holds 10,000 units of energy, how much reaches the rabbit (10%)? How much reaches the fox?
6. Discuss: why can a food web support far fewer foxes than rabbits?

Living thing	It eats	It is eaten by	Affected if rabbits disappear? (yes/no)
Grass
Rabbit
Fox
Snake
Hawk

Questions

1. Draw a food web with at least five living things. Label the producer and the apex predator.

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2. Explain the difference between a food chain and a food web.

3. Grass holds 20,000 kJ of energy. Using the 10% rule, how much energy reaches the fox in grass → rabbit → fox?

4. Why are food chains rarely longer than about five levels?

Sources for every fact on this sheet: echoesof.science/school/food-chains/sources/

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