Photosynthesis: how a plant makes food
The word equation for photosynthesis, how water travels from root to leaf, and stomata. With a coloured-water flower experiment.
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Plants are producers: they make their own food. Animals are consumers: they depend on plants, either by eating them or by eating animals that ate plants.[2]
The process is called photosynthesis ('putting together with light'). In words: carbon dioxide + water → glucose + oxygen, powered by light energy.[1]
It happens mainly in the leaves, inside tiny green parts of the cells called chloroplasts. The green pigment chlorophyll traps the light.[1]
Water enters through the roots and travels up thin tubes called xylem to the leaves. Water evaporates from the leaves (transpiration), which pulls more water up the stem, like sucking on a straw.[3]
Leaves have tiny holes called stomata. Carbon dioxide goes in and oxygen comes out through them.[1][3]
The glucose is the plant's fuel. Other tubes, the phloem, carry the sugar to the parts that are growing or storing food, like roots, fruits and seeds.[2][3]
Try it: The coloured-water flower
You need
- A white carnation, white chrysanthemum or a stick of celery with leaves
- Two glasses of water
- Food colouring (blue or red works best)
- Scissors (adult only) or a table knife
- A magnifying glass
Safety
Only an adult uses scissors or knives. Food colouring stains clothes and hands: wear an apron and cover the table.
What to do
- Add 20 drops of food colouring to one glass of water. Leave the other glass plain as a control.
- Ask an adult to cut the bottom 1 cm off the stems, so the tubes are fresh.
- Stand one flower or celery stick in each glass.
- Check after 1 hour, 4 hours and 24 hours. Where does the colour appear first?
- Next day, an adult cuts across the celery stem. Look at the cut end with a magnifying glass: can you see coloured dots?
What happens, and why?
The coloured water is drawn up through the xylem tubes, all the way to the petals or leaves. The dots on the cut stem are the xylem tubes themselves. Water evaporating from the leaves keeps pulling more water up.[3]
Play: Inputs and outputs
Is each thing something photosynthesis takes in, something it gives out, or a part of the plant where it happens? Pick the box.
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 15–16