You know the roots drink water. But how does the water get all the way up to the leaves? It climbs up the stem!
Key idea
The stem holds the plant up and carries water up and food down. The leaves catch sunlight and make the plant's food.
Why it works
Leaves need light to make food, so the stem lifts them up toward the sun. Inside the stem are tiny tubes, like drinking straws. Water rides up the tubes to the leaves. Food made in the leaves travels down to feed the roots.
Worked example: Let's think it through
A white flower stands in a cup of water with blue food coloring. The next day its petals have blue edges. How did the blue get there?
- The bottom of the stem was in the blue water.
- Tiny tubes in the stem carried the water up.
- The water reached the petals, and the blue color came along.
Answer: Up through the stem.
Common mistake
Some children think a stem is just a stick with no job. It is the plant's pipe and its pole. A tree trunk is a stem too: a big, woody one.
For the grown-up. Try the blue-flower test with a white carnation, a daisy, or a stalk of celery (celery's stalk holds up its leaves and works the same way). Use a fresh cut and a few drops of food coloring, and check the next morning.