This lesson is a great way to get students thinking about the world around them and what changes it goes through. It provides an opportunity for students to analyze the surroundings they see everyday and ask, "Why does this occur?". Specifically, this experiment deals with why leaves change colors. The green color of spring and summer leaves is caused by a green pigment called chlorophyll. However, in the fall, some leaves are not green. How does this color change occur? Pigments different from chlorophyll cause the beautiful reds, oranges, and yellows that we see in the fall. Are these pigments actually present in leaves throughout the year but hidden in the spring and summer? If so, then what hides the colors? Or are these red, orange and yellow pigments newly synthesized in the fall? This experiment will show indeed what happens. If the first scenario is true, and chlorophyll is the substance that hides the colors of the autumn pigments during the spring and summer months, then chlorophyll should not be present in colored fall leaves, but both green and colored pigments should be present in spring and summer leaves. However, if the second scenario is true, then the colored pigments would not be present in the spring and summer leaves. Their presence would be detected only in the autumn leaves.

As a review of the changes in seasons, ask the students to think about the color of leaves that they see in the summer and the color of leaves that they see in the fall. Once they have recognized that the green leaves turn into beautiful autumn colors such as red, orange, and yellow, ask the students if they can think of what makes the color of leaves change. After hearing their suggestions, explain the terms, "chlorophyll" and "carotene" (see vocabulary list below). Then suggest the two models of why leaves change color -- one, the colored pigments are present throughout the year, but chlorophyll hides them during the spring and summer -- or two, the colored pigments are newly made during the fall and, therefore, cause the color change. Tell them that there is a scientific procedure for determining the presence of individual pigments in leaves. Ask them to brainstorm how they could test which model of how leaves change colors is the correct one. After a class discussion, have the students write down their hypothesis for which model would cause the color change and what the results would look like for their model.

chlorophyll (green pigment)

carotene (fall color pigments e.g. red, orange, and yellow)

for each group of students:

• a green leaf and a yellow leaf taken directly from the same living tree in autumn (You can also use other colored leaves but a birch tree seems to work best.)
• quarter
• (2) 1" x 3.5" strips of filter paper
• beaker
• 71% isopropyl alcohol (rubbing alcohol)
• paper towel
• paper and pencil to record observations (green and yellow crayons would also be helpful)

Divide the class into groups of 34 and give each group a green and yellow leaf. Each group will then perform the following steps:

1. Place one of the filter paper strips down on the desk, and lay one leaf at the bottom.
2. Rub the rough edge of the quarter back and forth over the leaf so that a colored line appears on the filter paper approximately a centimeter from the bottom edge of the paper.
3. Cover the bottom of a beaker with the alcohol. (The depth of the alcohol should not exceed the height of the "leaf line" when the filter paper is placed in the beaker in the next step.)
4. Hold the strip of filter paper vertically in the beaker (edge of paper should touch bottom of beaker). Hold the paper steady until the liquid moves about 1/2 way up the filter paper.
5. Remove filter paper and lay it down on a paper towel to dry.
6. Repeat steps 1-5 for the other leaf.
7. Draw a picture of each filter paper strip including the band(s) of color that appeared.

Discuss the results in individual groups first, then as a whole class. Make sure the students can explain why the leaves change colors using the vocabulary words above. Also make sure they understand which of the two models their results support.

Have each group submit a lab report including their hypothesis, drawings, and conclusion.

Have students think about what effect the changing colors has on them. For example, maybe they know fall is coming when they see the leaves changing colors, and perhaps there is something special about fall that they like (the colder weather, crunching through fallen leaves, seeing the pretty colors . . . ) The children could write a story about these effects.

Another interdisciplinary project that the children could do is to write a story from the point of view of a leaf as it changes colors.

The students could do a unit on classification of leaves -- i.e., collecting a bunch of leaves from all different areas and classifying them according to certain properties.

Finally, the children could explore other changes that the leaves go through during the changing seasons (falling off the tree, growing from a bud etc. . . ). They could identify these changes and investigate why they occur.

SCIENCE CONTENT STANDARD #1: NATURE OF SCIENCE

This experiment is a great way to fulfill Benchmark I for grades 5-8 which states that students should "design, modify, and conduct an investigation through testing, revising, and occasionally discarding ideas, all of which lead to a better understanding of how things work." It also satisfies Benchmark 3 which states that students should "collect and summarize data from an experiment and interpret the results in terms of the data."

SCIENCE CONTENT STANDARD #2: PHYSICAL SETTING

Experimenting with how leaves change colors during the fall satisfies Benchmark 5 for grades K-4 which states that students should "observe how materials change over time."

SCIENCE CONTENT STANDARD #3: LIVING ENVIRONMENT

This standard states that students should "develop an understanding of the characteristics and life cycles of organisms and their environments." In this experiment, the students learn about the characteristics of leaves and how they change colors.

This experiment would tie in well with an earth science unit on the seasons. It could also be incorporated into a biology unit on plants. Finally, if the suggestions in the "Extensions" section are used then the experiment could be used in an interdisciplinary unit on science and language arts.