Transcript: Photosynthesis

NARRATOR: All life must have nourishment to live and grow. It's usually easy to tell where an animal's nourishment comes from. But what do plants eat?

Simply watching a plant won't give you the answer. They don't have mouths. Because plants grow up from the ground, people used to think plants ate soil for nourishment.

In the early 1600s, a Belgian scientist, Jan Baptist van Helmont, set out to discover for himself if this was true. Helmont planted a small willow branch into a pot of soil that weighed 200 pounds. For two years, he gave his tree only water. It gained 164 pounds. The soil, however, lost less than a pound.

The experiment convinced Helmont that plants get their nourishment from water, not soil. And he was partly right.

We now know that plants don't eat food the way animals do. They make food inside their cells. It happens in these tiny green bodies called chloroplasts in a process called photosynthesis. Photosynthesis is the source of all our food and all our oxygen.

A chloroplast is like a tiny factory. As Helmont saw, one of the key raw materials is water. But he couldn't see the other raw material, an invisible gas in the air called carbon dioxide. The chloroplast uses the energy in sunlight to combine the carbon dioxide and the water into a kind of sugar, called glucose. The sun's energy is stored in the glucose.

The reaction also makes oxygen, which is released into the atmosphere. The plant uses the sugar's energy to make all the other materials it needs to grow. By eating the plant, we can take a bite of all that stored solar energy and use it to power our own lives.