Experiment 3

How rapidly does a plant make starch?

Picture of a geramiumMaterials:

Tincture of iodine


Geranium plant



Graduated cylinder (A test tube marked in milliliters [ml]– borrow from a high school chemistry lab)

Black paper

Paper clips

Do this first:

1.    Place the geranium in a dark closet for 2- 3 days. The leaves will begin to turn white.

2.    Make an iodine solution by adding 5-ml iodine to 45-ml water.

3.    Test the potato of starch. Place a few drops of iodine solution on the potato. If it turns blue it has starch in it!

4.    Now test a white leaf from the geranium by crushing it in a small amount of water. What happens? Test the sugar. What happens?

5.    Remove several leaves from the geranium. Cover in places with black paper strips and place in the sun for 2 hours. How long does it take for the leaves to turn green? Now test the leaves for starch again.

What happens to the leaf under the black paper? Test it for starch too!


Test different foods for starch. Do some plants have more starch than others? Where did the starch come from?

Can you trace your dinner back to the sun?