Abstract

Objective

In this experiment you will test if the color or wavelength of light will affect the chlorophyll content of a leaf.

Introduction

Plants make food in their leaves using energy from the sun. How do they take the sun's energy and change it into food? They use a molecule called chlorophyll that is present in the leaves and makes them look green in color. Chlorophyll captures energy from the sun by absorbing rays of light that travel in waves.

Light traveling in a wave has a wavelength, which is a measure of the cycles of the wave. Light comes in different wavelengths, which to us look like different colors of the rainbow. Each color of light has it's own unique wavelength. The reason we see a rainbow of different colors is that each wavelength of light is separated from the others when they travel through the droplets of rain water, revealing a rainbow of different colors.

How do plants absorb different wavelengths of light? There are two types of chlorophyll, chlorophyll a and chlorophyll b, that each absorb different wavelengths of light and work together to give the plant energy to use to make food. Plants need to continuously make the chlorophyll in their leaves in response to light. In this way, the light acts as a signal to the leaf to make more chlorophyll.

Which wavelengths of light do leaves respond to? Are some wavelengths of light more important than others? What happens to leaves that don't receive any light? In this experiment you will investigate these questions using the leaves from your favorite houseplant.

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• light
• wavelength
• color
• photosynthesis
• chlorophyll

• Do plants use all of the colors of sunlight to make food?
• What happens to the leaf if one color is missing?
• What happens to the leaf if all of the light is missing?
• How are color and light related?

Bibliography

• Visit the website of "The Great Plant Escape" to help Detective Le Plant solve 6 cases, learn about plants, use the glossary to learn new terms and see pictures of plant parts:
  Stack, Greg, et. al. 2005. "The Great Plant Escape." University of Illinois, Urbana-Champaign. [12/13/05]
  http://www.urbanext.uiuc.edu/gpe/index.html
• VanCleave, Janice. 1993. Janice VanCleave's A+ Projects in Biology. New York, NY: John Wiley & Son's Inc. pp 107–112.
• Tero, P. & McTavish, T., 2000. "Single Filter Emission Java Applet," Berkeley, CA: ChemConnections, UC Regents. http://mc2.cchem.berkeley.edu/Java/single/Java%20Classes/single.html [accessed: 3/18/06]
• Eldridge, D., 2005. "The effect of light colour and intensity on the rate of photosynthesis," Scotland: Science and Plants for Schools (SAPS). http://www-saps.plantsci.cam.ac.uk/articles/broad_light.htm [accessed: 3/18/06]

Materials and Equipment

• clear transparency film
• permanent markers: red, green, blue, yellow
• black construction paper
• scotch tape
• healthy, leafy green houseplant: geranium, philodendron, ivy, etc...
• a sunny window

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Experimental Procedure

1. In this experiment you will be covering the leaves of your houseplant with sleeves of differently colored clear plastic, or with black construction paper as a control group. First you will need to make the different colored sleeves for your experiment.
2. Using your permanent marker, color one sheet of transparency film completely with each color. When you are done, you should have one red sheet, one yellow sheet, one green sheet, and one blue sheet. You will also need to keep one clear sheet as a control group.
3. Cut the different colored sheets (clear, green, yellow, blue, red, and black) into six squares by cutting each sheet in half along the length and into thirds along the width.
4. Place two squares of the same color together and tape with the scotch tape along three sides, making a sleeve. When you are finished you should have three sleeves of each color.
5. On your houseplant, place the sleeves over the leaves one at a time. Try to space the different colored sleeves out upon the plant. Each time, secure the sleeve to the stem by taping the open side shut with scotch tape.
6. Place the houseplant in a sunny window for one week, rotating the plant every day.
7. After one week, carefully remove the sleeves from the plant one at a time, each time noting the color of the sleeve and the appearance of the leaf in a data table:

   Sleeve Color	Leaf #1	Leaf #2	Leaf #3
   Clear
   Blue
   Green
   Yellow
   Red
   Black

8. Now look at your data and analyze your results. Remember that the color of the sleeve is the same as the light that is being ABSORBED by the leaf, not the color that is being BLOCKED from the leaf. The exception is the black sleeve, which is blocking all of the colors of light from being absorbed by the leaf.

Variations

• How long does it take the leaf to respond to the changes in light? Do a similar experiment using the black sleeves, removing the sleeves at different times and recording when the changes take place in the leaves. You can also do this experiment on several different types of houseplants to see if some plants respond faster or slower than others. Also try a similar timed experiment to test the recovery of the plant afterwards.
• In this experiment, we suggested that you use a leafy green houseplant. However, there are some species of plants that have non-green leaves year round. Try this experiment on a non-green leafy plant (it may need to be an outdoor plant, which is okay). Do the non-green leafy plants have a similar response to the changes in light absorption?
• Plants need their leaves to make food, which is stored in the roots and used for energy. How does the health of a plant depend on the amount of food made by the leaves? Take similarly-sized houseplants (philodendron are good for this experiment) and cover different numbers of leaves on each plant, ranging from few leaves to almost all of the leaves being covered. How does the health of the plant change depending upon the number of leaves blocked from the sun?

• For more science project ideas in this area of science, see Plant Biology Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Last edit date: 2006-03-21 19:00:33