A popular activity this time of year is to take a look at the changing leaves, marveling at the many colors you can find. But what causes green leaves to stop being green? And can you predict whether a leaf will turn red or brown? Let’s do an experiment to find out.
You will need: various leaves, a clear container for each leaf, rubbing alcohol, scissors and coffee filters. Try gathering some leaves that already have turned brown or other colors as well as some green ones so you can compare your results.
Tear each leaf into several pieces and put them in a clear container. Be sure to keep leaves from different plants separate and green leaves separate from ones that have already turned.
Pour enough rubbing alcohol into each container to cover the leaf pieces. The alcohol helps extract the pigments from the leaves.
Let your leaf pieces soak in the alcohol for a few hours. Observe the colors of the liquids. Is the liquid the same color as the leaf? Is it the color you expected it to be?
Then cut a coffee filter into strips. Insert one strip into each container. You want the bottom of the strip to be in the liquid and the top of the strip to be dry. This way as the strip absorbs the liquid, the liquid will move up the strip in a mostly straight line.
Let the strips soak up liquid for another few hours, then pull them out to see what color they have turned. What colors do you see on the strips? Is it the same as in the container or the same as the leaves?
You may notice that the leaves that already had turned made just one color on the strip, but the leaves that were still green made two colors on the strip. Why do you think that is?
Green leaves are green because they contain chlorophyll, an important molecule plants use in photosynthesis to get energy from light. As the weather cools and days shorten, many plants stop photosynthesis and use energy they have stored up, so they produce less chlorophyll.
As the leaves lose chlorophyll, they stop being green and any other colors they may have become more visible. Red and purple leaves have lots of glucose in them, left over from photosynthesis. Brown leaves are full of the plant’s wastes.
What color leaves did you start out with? Did they have chlorophyll, glucose, wastes?
And what colors do you have on your strips? If you have two colors on your strip, what does that mean? What does your leaf have inside it? If it started as a green leaf, what color will it be when all the chlorophyll is gone?
Take another walk back to wherever you collected your leaves in a week or two and see how things are changing. Did your experiment predict what colors you’d find?
Explorit’s coming events:
* Saturday, Oct. 19: “Touched by Science, Touched by Explorit: Celebrating 30 Years of Putting Hands On Science,” a fundraiser from 5:30 to 8 p.m. Enjoy food, wine, special guest speakers and get your own commemorative long-STEM wine glass! Explorit members and UC Davis Alumni Association members can purchase discounted tickets. Visit http://www.brownpapertickets.com/event/437033 to buy tickets.