From Seed to Seed:
Plant Science for K-8 Educators

Activity 16: The Quest for Light

Grades: 5-8

Associated Lesson Topics:

• Pigments and their role in photosynthesis
• Leaves changing color in the fall

National Standards:

• SCIENCE: Standard A, Standard C
• LANGUAGE ARTS: Reading 10

Planting the Seed...

What can you tell me about leaves? What do you think gives leaves their green color? Are all leaves green? What happens to leaves in the fall? How and why do you think they change from green to other colors? Do different-colored leaves have different pigments?

Teacher Information:

Pigments play a crucial role in photosynthesis. Without pigments, leaves cannot absorb the light that is necessary for photosynthesis. The pigments found in different types of leaves are different. In this activity, students will use a relatively simple technique-paper chromatography-to differentiate pigments.

This experiment is even more interesting if it coincides with the changing of leaves in the fall in temperate regions. Students can collect different-colored leaves and explore the answer to the above questions using paper chromatography.

Necessary Materials:

• Leaves from classroom/garden plants.
• Different colored tree leaves if you want to investigate the colors of fall foliage.
• Mortar and pestle.
• Acetone (nail polish remover).
• Test tube.
• Plastic wrap.
• Coffee filter.
• Scissors.
• Pigmentation guide.

Procedure:

• Students should collect leaves.
• Students should place a leaf in the mortar and add acetone. The amount of acetone added will depend on the size of the leaf. Next, they should grind the leaf with the pestle. The solution should resemble a leaf milkshake.
• Students should transfer the "milkshake" to a test tube.
• Students cover and leave overnight. During this time, the pigment molecules will dissolve in the acetone.
• Have students cut a coffee filter into ½-inch-wide strips. They should not use the perforated edges of the filter.
• Next, students place one end of the coffee filter strip into the solution and leave it overnight. During this time, the filter paper will absorb the solvent. As a result, the solvent will travel up the filter strip, carrying the pigments with it. Depending on the solubility of a pigment and its tendency to be absorbed, each pigment has a characteristic rate of movement. This allows the pigments to be separated out from one another on the filter strip because they "drop" out of the solution at different points.
• Students remove the strip from the solution and allow it to dry.
• Students can compare the strip to a pigmentation guide to determine which types of pigments their leaf contains.

Harvesting the Crop...

Students can research the role that each pigment plays in the plant. Are they all involved in light capture? We really only know the role of a few of the pigments found in plants. If students are unable to determine the role of some of their pigments, have them hypothesize what the role might be.

Sources

• Mortar and pestle, test tubes, pigmentation guide
  Carolina Biological Supply www.carolina.com

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