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Biological ScienceEcosystemsYear 3 Science

Food chains: who eats what, starting with a plant

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What this lesson covers

  • Plants make their own food from sunlight, water and carbon dioxide
  • Every food chain starts with a plant
  • Food passes along a chain when one living thing eats another
  • The arrows in a food chain point to the eater
  • Living things in a food chain depend on each other
  • A change to one living thing changes the others too
Key idea

Plants make their own food

  • Animals have to eat. Plants do not.
  • Plants make their own food.
  • They use sunlight, water from the soil, and a gas from the air called carbon dioxide.
  • The food is made in the leaves.
A plant takes in sunlight through its leaves, carbon dioxide from the air, and water from the soil through its roots, and makes food in its leaves
Key idea

What a food chain shows

  • A food chain shows who eats what.
  • It always starts with a plant, because plants make food.
  • Here is one: grass → rabbit → hawk.
  • The food, and the energy in it, passes along the chain from one living thing to the next.
Key idea

Which way the arrows go

  • The arrow means 'is eaten by'.
  • It points to the eater.
  • In leaf → caterpillar → bird, the caterpillar eats the leaf, and the bird eats the caterpillar.
Worked example

Example: a food chain in the bush

  • In the New Zealand bush, tree wētā come out at night to eat leaves.
  • Ruru, also called moreporks, catch and eat wētā.
  • Write the food chain.
A food chain of three boxes: leaves, then an arrow to wētā, then an arrow to ruru, with 'eaten by' above each arrow
  1. Start with the plant: leaves
  2. Leaves are eaten by wētā: leaves → wētā
  3. Wētā are eaten by ruru
  4. leaves → wētā → ruru
Worked example

Example: a food chain in the sea

  • Kina are spiky sea animals that eat kelp, a big seaweed. Big snapper eat kina.
  • Put these in a food chain: snapper, kelp, kina.
  1. Kelp is the plant, so it goes firstit makes its own food
  2. Kina eat kelp: kelp → kina
  3. kelp → kina → snapper
Key idea

Try it: where in the chain?

Key idea

Living things need each other

  • In a food chain, each living thing needs the one before it for food.
  • So if one changes, the others change too.
  • If the rabbits got sick and died, the hawks would have less food.
  • If the hawks were gone, there would be more rabbits, and they would eat more grass.
Key idea

Try it: change a forest food web

Worked example

Example: what if the snapper go?

  • People catch lots of snapper in one bay. Use the chain kelp → kina → snapper.
  • What happens to the kelp?
  1. Fewer snapper eat kina
  2. So more kina are left alive
  3. More kina eat more kelp
  4. The kelp gets eaten away, so there is less of it

Common mistakes

  • In grass → rabbit, the arrow means the grass eats the rabbit.
    The arrow points to the eater: the grass is eaten by the rabbit.
  • A food chain can start with any animal.
    Every food chain starts with a plant, because only plants make their own food.
  • Plants get their food from the soil.
    Plants make their own food from sunlight, water and carbon dioxide; the soil gives them water.
Try it at home

Make a hanging food chain

You need: 4 pieces of card, coloured pencils, a long piece of string or wool, sticky tape, scissors

  1. Go into the garden or a park with an adult. Find a plant and look for animals near it, such as a snail, a slater or a bird.
  2. Draw the plant on one card and one animal on each of the other cards.
  3. Tape the cards onto the string in order, with the plant at the top.
  4. Draw an arrow on each card pointing down to the next one, the eater.
  5. Check your chain: does it start with a plant, and does every arrow point to the eater?

Safety: Do not touch or pick up wild animals, and wash your hands after being in the garden.

Your turn

1

What three things does a plant use to make its food?

2

Put these in a food chain: hawk, grass, rabbit.

3

In leaf → caterpillar → thrush, what eats the caterpillar?

4

What is always at the start of a food chain?

5

In grass → rabbit → hawk, the rabbits get sick and die. What happens to the hawks?

Show answer

1. Sunlight, water and carbon dioxide. 2. grass → rabbit → hawk. 3. The thrush. 4. A plant. 5. The hawks have less food, so there will be fewer hawks.

Summary

Recap

  • Plants make food from sunlight, water and carbon dioxide.
  • A food chain shows who eats what, and it starts with a plant.
  • The arrow means 'is eaten by' and points to the eater.
  • Food and its energy pass along the chain.
  • Living things in a chain need each other, so a change to one changes the rest.
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