The Family Fun Rack Cards are activities designed for the whole family to enjoy while at the Morris Arboretum and at home. Fall's Rack card is called "Be a Plant Physiologist" and this web page is an extended and more advanced version of the printed card. Come visit the Morris Arboretum each season for new educational activities to enjoy as a family.

Why are leaves different colors during autumn?
Every autumn we see many leaves change color and fall to the ground. This physiological process, called leaf senescence, is marked by green leaves changing to brilliant hues of red, yellow, and orange. The colors we see in leaves result from pigments in leaf tissue reflecting certain wavelengths of visible light.

The green color of leaves is the result of a pigment named chlorophyll that reflects green wavelengths of visible light. Chlorophyll is found in chloroplasts, which are organelles specialized for photosynthesis - a process that harnesses solar energy and converts it to chemical energy stored in organic molecules, such as sugar.

During leaf senescence, chlorophyll degrades and is not replenished, which results in the appearance of other colors. These colors are produced by pigments carotene, xanthophyll, and anthocyanin. Carotene and xanthophyll, which create hues of orange and yellow, respectively, were created during the growing season and masked by chlorophyll. In contrast, anthocyanin, which creates red hues, is produced in autumn.

Leaves of different colors and from different types of trees contain different amounts of these pigments. Collect some different colored leaves from the ground at Morris Arboretum and try to guess what pigments these leaves contain.

Plant Physiologists are scientists who study how plants function. Start your Plant Physiologist career by separating the different leaf pigments in this experiment:

Do this experiment with an adult.

Always be careful when using sharp objects, like scissors and always work with an adult when dealing with rubbing alcohol and other chemicals. Read and follow warnings on the alcohol bottle.

Gather these materials from around the house:

Step One

Roll up the leaf and cut it into small pieces. Place these pieces into the small beaker (or cup).

Step Two

Pour rubbing alcohol into the small beaker so that the leaf pieces are barely covered. Tilt the beaker, swirl the solution and continue to cut the leaf into smaller pieces with the scissors. Tip: This experiment will work best if you can cut the leaf into very small pieces (the smaller the better) as more of the pigments will be released into the alcohol solution.

Step Three

Fill the large beaker (or bowl) with about 1˝ of hot water and place the small beaker into this hot water bath for about five minutes. The hot water will help the leaf’s pigments to be released into the alcohol - you should see the alcohol darken. Tip: slightly covering the smaller beaker will help the alcohol from evaporating in this step.

Step Four

Cut the coffee filter into a ½˝ wide strip. Wrap the filter around a pencil and secure with a paper clip so that the bottom of the filter hangs just above the bottom of the small beaker but dips into the alcohol. Tip: You want to make sure this coffee filter strip is as straight as possible - it might be easier to cut the coffee filter and adjust the length, before adding the leaf or alcohol.

Step Five

After about 30 minutes, remove filter paper from beaker and allow to dry. Notice different color bands on the filter - these are different pigments from the leaf that have been separated in this process called Chromotography.

Analysis

You should be able to observe different colored bands on the coffee filter. These pigments are responsible for the color of the leaf you used in this experiment.

Other Variations of this experiment:

Try this experiment again with leaves from:

Links:

Material Safety Data Sheet (MSDS) for rubbing alcohol (Isopropyl Alcohol)

Autumn Leaf Color