“Why do leaves change colors?” Someone replied, “They are getting old. They will all fall on the ground soon.” “Yeah, the trees will all be bare.” “Yes,” I said bringing us back to the original question. But why do the leaves turn colors?” Below is what I found:
Chromatography, is the separation of a dissolved mixture by passing through filter paper through which different parts of the mixture will move at different rates. The pigments that were more soluble in the solvent (water) moved further up the paper than the less soluble pigments.
Using the green leaf as an example, the blueish-green chlorophyll A was less soluble than the yellowish green chlorophyll B and thus it didn’t move as far up the paper. I set out to find a little more about it that night and then worked out a way to make it preschool friendly.
It was one of those crisp autumn days in Boulder where it is cold in the shade and hot in the sun. What a great day to get outside and do some hands on investigating. We rolled out the back door of the preschool, bundled up in hats and coats. The children hopped and skipped across the wide open soccer field in search of colorful leaves.
The children collected red, yellow, green and purple leaves. It was a little late in the season but soon we hauled our treasure back to the class room and sat down to sort them out by color.
With careful hands, there was a lot of discussion about which colors or “pigments” would climb up the paper towel. Each color is a different kind of food for the tree that was down in the soil. We talked about how trees take nourishment up through the roots, and through the leaves from the sun light. In the fall, the trees takes up less food from the ground and this effects chemicals in the dying leaves, so they change colors.
We then mixed the leaves up and chop them into tiny pieces so that the colors that were still in the leaves would creep up the paper and show us the strongest to weakest colors.
Each child had a turn with every step of the experiment. They voted on which color to start with, and then they loaded red leaves into the mixer. They poured in the water then and then turned on the loud machine. These children are not afraid of loud noises!
“Its leaf mush now!” We set the jars out to rest and mix. Later, each child dropped a strip of paper towel into the “mush”.
Over the next few days we watched the progress of the colors working up the paper. Other children from the class took some interest, and the kids shared stories about what they were doing. Some of the colors were a bust. The green turned a murky beige. In the end, the red and yellow gave the best show.
“The trees liked the red food from the ground.” A child murmured holding up the jar.