Why does a plant need more than water?
Have you ever poured water into a flowerpot and watched the dark soil soak it up? Press a finger into the soil afterwards, and you can feel how cool and damp it has become.
Water matters a lot to a plant. Yet if you give a plant only water, it will not grow big and strong. So why does a plant need more than water?
Water travels up the stem into every leaf. But growing bigger takes food, and water by itself is not food. A plant needs food, just like you do.
Look closely at a plant's leaves. Each flat green leaf spreads out wide to catch sunlight. The sunlight gives the leaf the power it needs to do its work.
Leaves also take in air through tiny holes, much too small for you to see. That air carries a gas that you breathe out, and the leaf can use it. Sunlight, air and water now meet inside the leaf, so what do you think the leaf makes with them?
The leaf makes its own food! Using the power of sunlight, it joins water and that gas from the air into a kind of sugar. Plants do photosynthesis, which means making food with light.
That sugar gives the plant energy and the stuff to build new leaves, stems and roots. Without sunlight, photosynthesis stops. If you keep a plant in a dark cupboard, it grows pale and weak, even with plenty of water.
A plant needs one more thing from below. Its roots take in nutrients, which means tiny bits from the soil that help a plant build its body. The nutrients mix into the water in the soil, and the roots drink them in together.
The plant uses nutrients to build green leaves and sturdy stems. Green leaves catch sunlight well, so nutrients help photosynthesis keep going too. In old, worn-out soil, the roots find too few nutrients, and the leaves turn yellow.
Photosynthesis, nutrients. A plant needs more than water because its leaves use sunlight and air to make food by photosynthesis, and its roots take in nutrients from the soil to build strong green parts.
Next time you water a plant, you can picture its leaves soaking up the light, busy making their own food.
