A plant gets all its water. Does it still need the sun?
A little plant sits by the window. We give it a nice drink of water… glug, glug. And the warm sun shines on its leaves. Now let's try something. We'll keep giving it water, but we'll move it into a dark, dark box with no sun at all. Ready to guess… will it stay green and happy, or will it go all droopy?
After you watchA plant gets all its water. Does it still need the sun?
The short answer
A plant needs the sun, not just water. Water is the plant's drink, but the sun is how a plant makes its own food in its leaves. With water but no sun, a plant slowly goes droopy and pale, because it cannot make food in the dark.
Try this next
- What if the box wasn't all the way dark, just a little bit dim? Imagine a box with one small window letting a little sun in. Guess first: does the plant stay happy, get a little droopy, or fully droop? Then think about how much food a little bit of sun could make.
- What if you gave the plant lots and lots of water but still no sun? Picture pouring in extra water every day in the dark box. Guess what the plant does, then think about whether more drinks can ever turn into food without the sun.
- What about a lamp instead of the sun? Imagine switching on a bright lamp over the plant in the box. Guess if a lamp can do the sun's job, then think about whether the leaf just needs light from somewhere to make its food.
The whole story
How it works
Roots pull up water and it keeps the plant plump, like a drink. But water is not food. A leaf uses sunlight to build its own sweet food right inside it. In a dark box there is no sunlight, so the leaf makes no new food. The plant runs out of food and droops, even with plenty of water. In the sun the leaf keeps making food, so the plant stays green and happy.
What people get wrong
Lots of little kids think water is a plant's food, so watering it is all it needs. But water is only the drink. The plant's real food is made by its leaves using sunlight. Take away the sun and a watered plant still goes droopy, because its food cannot be made in the dark.
The catch
Water really matters too — without a drink a plant wilts and dies. But water alone is not enough, because water is not food. The sun is what lets the leaf make food. A plant needs both the drink and the sun together to stay happy.
Questions kids ask
Why does a watered plant droop in the dark?
Because the sun is how a leaf makes its food, and there is no sun in the dark. Water keeps the plant plump but it is not food. With no food being made, the plant slowly goes droopy even though the soil is wet.
Is water a plant's food?
No. Water is the plant's drink. It keeps the plant standing up, but it has no food energy in it. A plant makes its own food in its leaves using sunlight, so it needs the sun too.
So does the plant need water at all?
Yes! A plant needs both. Without a drink it wilts and dies, and without the sun it cannot make food. The drink and the sun work together to keep the plant happy.
Talk about it
- We watered this plant every day, but we kept it in a dark corner and it drooped. What do you think it was missing?
- If water isn't a plant's food, what do you think the sun is really doing to the leaves?
- Could you live on just water with no food? What do you think a plant lives on?
For grown-ups
This is photosynthesis, dialed down for ages 4–6. In a leaf's chloroplasts, sunlight powers a reaction that combines carbon dioxide from the air with water into sugar — the plant's food. With no light the plant fixes no carbon and lives off stored food until it runs out, even in wet soil. The roots supply water and a few minerals, never the bulk food. We say 'the sun makes the food' and skip the words sugar, carbon dioxide, and photosynthesis on purpose.
Keep going
What else makes you wonder?
- If the plant could only have one — a drink of water or the warm sun — which do you think it would pick?
- What do you think happens if we put the droopy plant back in the sun? Could it perk up again?
- We made food with the sun. What else do you know that the sun helps make warm or grow?