Have you ever wondered why leaves change colors in the fall? We have too! That’s why we’re exploring leaf chromatography for today’s Tiny Club activity.
If you haven’t watched it already, be sure to check out our reading of Britta Teckentrup’s Tree, a peek-through picture book. This book shows a forest scene in different seasons, including a beautiful tree whose leaves change colors in the fall. Today, we’re going to do a simple science experiment to learn why leaves go from green to yellow and red in autumn.
A few different leaves (grab multiple kinds and colors if you can find them!)
A coffee filter
Rubbing alcohol (we used 70% isopropyl alcohol)
Step 1. Use your scissors to cut inch-wide strips out of your coffee filter. These will be your chromatography strips.
Step 2. Place your leaf on top of your chromatography strip near the bottom.
Step 3. Use your penny to rub a line across your leaf onto the chromatography strip. Do this about two inches above the bottom of your paper strip. Continue running the penny back and forth in a straight line until you have a green line across your paper.
Step 4. Fill your cup with less than one inch of rubbing alcohol.
Step 5. Gently place your chromatography strip into the liquid so that the end of the strip closest to your green line is the end that rests in the cup. You may need to use tape to prop the filter paper up so that it does not sink into the rubbing alcohol.
Step 6. Wait. The liquid should start traveling up the filter paper and should eventually reach the green line. You should start to see the color spreading up the filter paper and separating out. You may see green, lighter green, yellow, and even some red!
We used a process called chromatography to separate out the different pigments, or colors, inside our leaf.
Chromatography: The scientific process of separating a mixture.
Our rubbing alcohol allowed us to “unmix” or separate the different pigments inside of the leaves. Typically, those pigments are hidden by chlorophyll, which is the green, dominate color we see on our leaf. But when we separated out the chlorophyll, we are able to see the yellow and red pigments that had been hidden before!
But why do tree leaves change colors in the fall? Well, chlorophyll helps the tree absorb energy from sunlight. As the fall and winter months come, the tree receives less light and produces less chlorophyll. The chlorophyll starts to fade and those red and yellow pigments (also called anthocyanin and carotenoid pigments) are revealed. Eventually, the leaves fall off the tree! Then in the spring, when the weather is warmer and the tree receives lots of sunlight, the tree starts growing green leaves again.
When we did our experiment, we saw yellow pigment separate out from the green line. Our leaves had carotenoids, or yellow pigment, hidden in them. We were able to see some leaves on the tree that were already changing from green to a vibrant yellow!
Check back next week to learn how trees get their nutrients!