Illinois Natural History Survey - University of Illinois

Where Does the Green Go?: Download PDF

This information is taken from the Illinois Department of Natural Resources Kids for Trees. For more information and activities about trees, check their website.

SUBJECTS: Science, Math, Art, Language Arts
SKILLS: observing, gathering information
OBJECTIVE: Students will learn that leaves lose their green color as the days grow shorter and the weather becomes colder and that as the green disappears other colors become visible, while still new colors are created.

Leaves change color in the fall because the days grow shorter with fewer hours of sunlight. When there's not enough sunlight, the green chlorophyll cells in plants stop making food and break down. As they break down, chlorophyll cells lose their green color, but other colors that have been in the leaf all along then can be seen. Still other new colors are formed through new chemical reactions that become possible once the chlorophyll is gone.
chlorophyll.gif When the Little Green Food Factories Shut Down. All leaves have some yellow pigment in them, and many have red tones as well. But these colors can't be seen in the spring and summer because they are overpowered by the green color of chlorophyll. Chlorophyll cells need sunlight to do their job. Once there is not enough light, leaves stop producing food and lose their green color. Then the other colors can be seen. Leaves become yellow or brownish red. Many of the bright fall color have not been present all along. They are made once the chlorophyll is gone. Now other chemicals have a chance to react with sunlight. Bright red and purple colors are the result. The sugar maple, for example, is one of the most colorful fall trees. This is because the leaves are full of sugars that have been produced by the chlorophyll. The sugars react to the sunlight and to the cooler weather by turning bright colors.

The Best and the Brightest. All leaves change color before they fall from the tree. But some leaves are more colorful than others. Just as some people's hair changes as they get older, some leaves can only change to yellow or green. Weather conditions are another factor that affects the color of fall leaves. The best and the brightest colors occur in years that have wet summers, cool fall nights, and warm sunny fall days. In Illinois, the best and the brightest fall trees are hard maples, red oaks, ash trees, sweet gum trees, and sassafras trees.

At the beginning of the school year have each student bring in a leaf from the tree of his or her choice. Have students press the leaves between newspaper sheets and then mount them on a piece of paper, preferably under clear adhesive plastic, leaving room for a companion leaf. In the fall, after the leaves have changed, have each student bring in a leaf from the same tree. Press and mount alongside the original leaf and have the class discuss the variety of colors represented or write a poem about the changes that have occurred.

Using watercolors, you can show how the green chlorophyll pigment in leaves can hide other colors. Start with yellow and cover it with green. What happens? Start with red and cover that with green. Again, what happens? Now discuss what would happen if the green were removed. This can also be done with colored acetate swatches and an overhead projector.

Have children bring to class pictures from magazines that depict colorful fall scenes. Compare the pictures. Are the colors the same? Why are they different are they from different localities, different types of trees? Can students determine, with a good tree identification book, which trees are pictured?

Make a chlorophyll leaf print. Place a leaf between two pieces of white paper, place a board over it and pound with a hammer. This will bring out the chlorophyll and leave a green impression of the leaf. Make prints of several kinds of leaves and discuss the different shapes and details.

Take the class on a brief neighborhood color walk. Have younger children identify colors. Older children may make a list of different colors that can be seen and tabulate the number of times each color is viewed or spotted.

Have students bring in the most interesting leaf shape they can find. Trace it and color it in its summer colors and in its fall colors. Paste a selection of these leaves on one crazy tree poster, or make a collage of interesting colors and shapes. Cut leaf tracings in half and have children match shapes.

Divide the class into small groups. Each group should discuss and arrive at an answer to this question: If leaves fall off in the autumn, why do they come back in the spring?

chlorophyll, pigment, chemicals, chemical reaction, cells

Next lesson - What Do Trees Do for Dinner?

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