Experiment: Colors in a Leaf
September 24th, 2014
In honor of the first day of autumn, I decided to post a fun little science project anyone can do at home. With just a few household items, you can get a sneak peak at the autumn colors inside just about any green deciduous leaf.
When a leaf changes colors if fall, it doesn’t gain a new pigment. Instead, the green chlorophyll used to make food from sunlight starts to dwindle as the days grow shorter and the leaf reaches the end of its lifetime. Pigments that were masked by the chlorophyll in spring and summertime become more noticeable during fall. Some of these pigments include xanthophyll (yellow), carotene (orange), and anthocyanin (red). We can use a process known as chromatography to parse out all the colors in a leaf.
You may or may not need to go to the grocery store for these items.
- Green leaves from a deciduous tree (a.k.a. broad leaf tree)
- Isopropyl alcohol (a.k.a. rubbing alcohol)
- Small cup or jar (jam jars work well)
- Paper coffee filters
- Masking tape
- Coin (quarters work well)
Estimated Time: 90 minutes
Warning: Assuming you aren’t the brightest bulb, be warned that rubbing alcohol is toxic. Do not ingest! To be on the safe side, please don’t ingest your leaves either!
With your materials ready and a clean workspace, let’s begin!
Use the scissors to cut the leaves up into small pieces. For best results, use a ￼mortar and pestle to grind the leaves into a paste. Try to extract as much of the leaf’s pigment as possible.
Put the leaf scraps in the jar. Then pour just enough rubbing alcohol into the jar to cover the leaf scraps. Let the mixture sit for about twenty minutes. This allows the rubbing alcohol to absorb enough pigment from the leaf scraps. (To speed up the process, place the jar in a hot water bath. Heat makes the rubbing alcohol a more effective solvent for dissolving the leaf pigments).
￼While you wait for the pigments to dissolve, cut a rectangular strip out of the ￼paper coffee filter. Then tape one end of the paper strip to the pencil. The paper strip ￼and pencil should resemble the letter “T.”
When the rubbing alcohol has attained a deep hue, place the pencil with the paper strip on the mouth of the jar such that the paper strip is hanging over the liquid and partially submerged. Leave the apparatus alone for at least an hour. During this time, capillary action will work its magic, drawing liquid upwards and separating the pigments into distinct bands. The results may be reminiscent of a beautiful sunset.
When the process is finished, remove the paper strip from the apparatus. Allow the chromatograph to dry. Then try to identify the various pigments in your leaf. The “spectrum” will vary based on the type of leaf you chose. Optionally, you can save your chromatograph as souvenir. Store it somewhere safe and dry (e.g. tape it in a notebook).
Before I began the experiment, I predicted that the cherry plum leaf would show a lot of anthocyanin in the chromatograph since the leaves are reddish purple all year around. I was surprised to see so many yellow and orange pigments in the results. Not surprisingly, there was a relatively small amount of green pigment.
The sweetgum leaf showed fewer red pigments than I expected. I predicted that the sweetgum chromatograph would show a lot of yellow pigment since I have seen the sweetgum trees turn brilliant yellow in autumn. I noticed two distinct bands of green (chlorophyll A and chlorophyll B).
For more information on leaf pigmentation, check out the links below.
“Leaf Pigments.” Harvard Forest. 2011.
Nave, R. “Pigments for Photosynthesis.” HyperPhysics. 2014.