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Primary Science · Year 3Chapter 3 · What plants need
Year 3 Science · What plants need · Lesson 3.2

Year 3 Science: Light and air: making food in the leaves

Part of the Year 3 Science what plants need chapter. Chapter overview · whole chapter on one page

3.2

Light and air: making food in the leaves

Year 3
Explore the requirements of plants for life and growth: light and air, and how leaves use them to make food
Story. Chloe holds a bean leaf up to the classroom window. “Why does the leaf need light?” she asks. Kofi points to the leaf. “And it gets air through little holes, doesn’t it?”

Plants need light to make food. Leaves catch light, and they use it, together with water and a gas from the air, to make food for the plant.

The gas from the air is called carbon dioxide. Leaves take it in through tiny holes, which are mostly on the underside of the leaf. Plants also give out oxygen, which is a gas that people breathe in.

A plant in a dark place cannot make food from light. It may grow weakly, and its leaves may look pale and thin.

lighttop of leafundersidetiny holesair goes in
A leaf: light falls on the top, and air goes in through tiny holes, mostly on the underside.

Key ideas

  • Leaves use light, water and carbon dioxide from the air to make food.
  • Carbon dioxide is a gas in the air.
  • Leaves take in air through tiny holes, mostly on the underside.
  • A plant in the dark cannot make food from light, so it grows weakly.
Worked example 3.2.1
Which gas do leaves take in from the air to make food? Write the gas.

Method. Think about the gas that leaves take in through their holes.

  1. Read the question. The question asks for the gas that leaves take in from the air.
    gas from the air
  2. Think about the holes. Leaves take in a gas through their tiny holes.
    tiny holes
  3. Name the gas. The gas that leaves take in from the air is carbon dioxide.
    carbon dioxide
  4. Write the answer.
    carbon dioxide

Check. Plants take in carbon dioxide and use it to make food. ✓

Worked example 3.2.2
Two bean plants are kept for three weeks. Plant A is on a sunny windowsill, and plant B is in a dark cupboard. Which plant is more likely to be pale and thin? Write A or B.

Method. Think about which plant can use light to make food.

  1. Read A. Plant A is on a sunny windowsill, so it gets light.
    A: light
  2. Read B. Plant B is in a dark cupboard, so it cannot make food from light.
    B: no light
  3. Choose the plant. The plant that cannot make food from light is more likely to be pale and thin.
    B
  4. Write the answer.
    B

Check. A plant in the dark grows weakly. ✓

Watch out. The plant in the light is not the pale one, because it can make food.

Worked example 3.2.3
Sarah says plants do not need air, because they only need light and water. Is Sarah right? Write yes or no.

Method. Check the list of needs.

  1. Read the claim. Sarah says plants only need light and water.
    light and water only
  2. Check the list. Plants also need air, which leaves use to make food.
    air is needed
  3. Decide. So Sarah is not right.
    no
  4. Write the answer.
    no

Check. Air is one of the five needs of a plant. ✓

Watch out

Watch out: leaves do not take in carbon dioxide through their roots. They take it in through tiny holes, mostly on the underside. The roots take in water and nutrients from the soil.

Try it at home or school (with a grown-up). With a grown-up, look at a leaf from a houseplant or a tree, using a magnifying glass. Gently look at the underside. Can you see any tiny holes? Some leaves show them more clearly than others. Draw the leaf and label the top and the underside. Do not pick the leaf. Wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “Which side of the leaf gets the light? Which side might the air go in through?” Let your child show you where the tiny holes are, if they can see them.

Exercise 3B  Light and air: making food in the leaves

1
FLeaves take in a gas called carbon ___. Write the missing word.
2
FLeaves use light to make ___. Write the missing word.
3
FWhich gas do plants give out that people breathe in? Write the gas.
4
FLook at the leaf picture. Are most of the tiny holes on the top or the underside of the leaf? Write top or underside.
lighttop of leafundersidetiny holesair goes in
5
FFill in the gaps.
(a)Leaves use light, water and carbon dioxide to make ___.
(b)Plants in the dark grow ___.
6
FWhich bean plant is more likely to be healthy: the one on the sunny windowsill, or the one in the dark cupboard? Write the one.
7
PSMia counts 9 green leaves on a plant on the windowsill, and 3 pale leaves on a plant in a cupboard. How many more leaves does the windowsill plant have?
8
PSRuby says a plant in the dark will make as much food as a plant in the light. Is Ruby right? Write yes or no.
9
PSWorking scientifically. Plan a test to find out whether light helps a leaf to make food. Write one thing that you must keep the same for both plants.
10
RIs this true or false? Leaves take in oxygen from the air to make food. Write true or false.
11
RExplain in one sentence why a plant on a windowsill grows better than one in a cupboard.

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