Rocket sets a bag of potting soil on the workshop scale. "Plants eat dirt," he says. "Everyone knows that."
Raven frowns. "The oak by the creek is huge. Is there a giant hole under it?"
Rocket opens his mouth, then closes it. "No. The ground is flat."
Nova projects a tiny cyan tree that grows taller and taller. "So where did all that wood come from?"
Hundreds of years ago, a scientist wondered the same thing.
He weighed a tub of dry soil. He planted a small willow tree in it.
For years he gave the tree nothing but water. He kept dust off the soil.
The tree grew big and heavy. Then he dried the soil and weighed it again.
The soil weighed almost exactly the same as before.
The tree had gained a great deal of weight. The soil had lost almost none.
So the stuff of the tree did not come from the soil. It had to come from somewhere else.
A plant is built mostly from two things: water and a gas from the air.
Roots take in water from the ground.
Leaves take in a gas called carbon dioxide from the air.
In the leaves, light gives the energy to join water and carbon dioxide together.
The plant makes sugar. This is called photosynthesis. Photo means light.
The plant uses that sugar for energy and to build new parts.
Leaves, stems, wood and roots are all built from that sugar.
While it does this, the plant lets out oxygen. That is the gas we breathe in.
| Statement | True or false? |
|---|---|
| Plants are built mostly from soil. | ? |
| Leaves take in carbon dioxide from the air. | ? |
| Light gives plants the energy to make sugar. | ? |
| Plants let out oxygen. | ? |
Big idea, well done! Tomorrow we watch water climb a stem with our own eyes.