How plants make food — Biology, 7–10 years
Green leaves use light to make sugar from water and carbon dioxide. This is how a plant gets much of its food.
Leaves are tiny food-makers
A green plant does not eat a sandwich or drink juice for food. Its leaves use light energy to join water from the roots with carbon dioxide from the air, making sugar. The sugar gives the plant energy and building material; oxygen is released into the air as well.
Why do leaves need light?
A plant can take in water and air, but those ingredients do not become food by themselves. Light supplies the energy for the change. This explains why a plant kept in darkness may stay alive for a while using stored food, then become pale and weak when its store runs low.
A simple plant test
Cover one leaf of a potted plant with dark paper, leaving another leaf uncovered. Put the plant in daylight for two days, then remove the paper. The covered leaf received water and air but little light, while the other received all three. The difference shows that light is needed to make food.
The plant-eating mistake
Because people call sugar and starch “food”, it is tempting to think a plant must take food in through its roots. Roots mainly take in water and minerals, while leaves make sugar using light and air. A plant can still use minerals from soil, but minerals are materials for healthy growth, not its main energy food.
Why plants matter to us
Plants make their own food, but they also support many other living things. People eat plants directly, and animals eat plants or eat animals that ate plants. Growing plants also helps add oxygen to the air and provides materials such as wood, cotton and fruit. This is why healthy plants matter beyond a garden.
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