Our Autumn Leaf Lab

This year we seemed to have just enough good weather conditions to have beautiful fall colors for Washington state (warm days, cool but not freezing nights).

Working our way through the Periodic Table, we came to magnesium, which is to chlorophyll as iron is to hemoglobin.

These are easy experiments, and if you have autumn leaves, it's a perfect time to do them. Pluck a variety of leaves, cut or tear them into cups. Add alcohol (isopropyl, ethanol, or even alcohol-containing hand wash will do in a pinch) and mash them up with a spoon. Cover with foil and let stand for 1 hour. Then cut strips of coffee filters into the solution and watch for colors that migrate up the filters.


We generated hypotheses before starting the experiments. Hypothesis #1: In plants that drop their colored leaves, the change in color is due to a loss of pigment, rather than an increase in pigment (for instance, yellow leaves have lost their green, not gained yellow). Hypothesis #2: Plants with colored leaves that do not drop have an increase in a new pigment rather than pure loss.

I'm not completely sure you can see the results, but it was interesting. For the red and purple bushes, we could see an extra band of blue that wasn't present in the green or yellow leaves. Chlorophyll a is blue-green and chlorophyll b is yellow-green. It seemed as if the red and purple leaves had chlorophyll a.

We also made other observations as through the course of the experiment. We found the yellow leaves were the easiest to dissolve with alcohol (due to early breakdown of their cell walls?) and thought about the various designs of the leaves. The big maples seemed particularly well designed to catch sunlight (large surface area), but perhaps the addition of blue chlorophyll conferred some energy advantage on the smaller red leaved bushes? Also the bushes had more leaves and were much smaller than the big maples.

When we looked back at our hypotheses, it looked like the behavior of the green and yellow leaves supported Hypothesis #1. Although it doesn't show clearly in the picture, we extracted much more chlorophyll from the green leaves than the yellow. Hypothesis #2 was less clear because we used two red / purple-leaved bushes, one that dropped its leaves, and one that didn't. Both seemed to have both yellow-green and blue-green chlorophyll, and we couldn't determine quantity. Not surprising, more sampling would be necessary to determine something like this!

Early Science and the Study of Chlorophyll and Photosynthesis
Science of Fall Color pdf