Autumn Leaves

This activity takes a look at autumn leaves as objects of aesthetic beauty and scientific interest. Part 1 of the activity is designed for elementary school students and focuses on the aesthetic beauty of autumn leaves and their value as craft materials. Part 2 of the activity is designed for middle school students and explores the pigments that give autumn leaves their flamboyant colors. It can be used to address the following National Science Content Standards in life science: 5–8 Structure and Function in Living Systems and 5–8 Regulation and Behavior.

Part 1: A craft project using autumn leaves

For this activity, each of your students uses colorful autumn leaves they have collected to create a decorative arrangement on a sheet of waxed paper. You then cover each arrangement with another sheet of waxed paper and seal the 2 sheets together with a hot iron. The sealed arrangements can be used in placemats, mobiles, or decorations.

Materials

• A household iron
• A one-hole paper punch
• An assortment of colorful autumn leaves
• Blunt-tipped scissors
• Waxed paper

Procedure

Safety note: Keep your students away from the hot iron and do not allow them to touch their arrangements until they are cool.

1. Make sure each student has 2 equal lengths of waxed paper about 18" long and an assortment of colorful autumn leaves.
2. Have your students creatively arrange the leaves (without overlapping them) on one of the sheets of waxed paper.
3. Place some spare leaves between 2 sheets of waxed paper. Set the iron to its lowest temperature setting and briefly place it on the top sheet of waxed paper. If the 2 sheets of waxed paper do not seal together, gradually increase the iron's temperature setting until the sheets seal together without scorching.
4. Place a sheet of waxed paper over each student's arrangement and seal it with the iron. Keep your students away from the hot iron and do not allow them to handle their arrangements until they are cool. When the arrangements are cool, students can trim them with scissors if needed.
5. To make a mobile or individual leaf collection, have your students cut the waxed paper into pieces big enough to allow for a 1" margin of paper around the leaves.
6. Seal each leaf as described in step 4.
7. Have your students trim the cooled leaves leaving at least a 1" margin of waxed paper around each leaf. For mobiles, use a one-hole paper punch to make an attachment point in the margin of waxed paper.

Extension activity

Assign groups to study different types of trees, and then create a classroom forest with your groups of oaks, maples, aspens, or evergreens. Have each group talk about the bark, leaves, folklore, and other characteristics of their tree. If your campus has trees on it, allow the groups to continue their observations by creating a calendar of events for their trees, e.g., when the leaves start to fall and when all have fallen, when the buds for flowers or leaves appear in the spring, when it produces fruit, and what animals inhabit it.

Part 2: Exploring plant pigments

The shorter days and cooler temperatures of autumn trigger a slowdown in a tree's metabolism, reducing its chlorophyll production and the flow of water and nutrients within its trunk and branches. Its leaves turn color because the reduced production of chlorophyll allows other less-dominant pigments to be revealed.

Chlorophyll, carotenoids, and anthocyanins are the basic pigment groups responsible for plant colors. There are many types of each of these pigments, and they can be broadly grouped by water solubility. Anthocyanins are water soluble, but chlorophyll and carotenoids are not. This activity will help you determine if a plant pigment is water soluble.

Materials

• Cutting board
• Ethanol
• Flower petals, leaves, vegetables, and fruits
• Kitchen knife
• Test tubes
• Water

Procedure

Safety notes: Use caution when chopping specimens with the knife. Keep ethanol away from open flames and other sources of ignition.

1. Select a variety of flower petals, leaves, vegetables, and fruits to test.
2. Chop each specimen finely (you may want to do this for middle schoolers) and divide it in half.
3. Place a small amount of a specimen in 2 test tubes.
4. Add water to one of the tubes; just enough to cover the chopped specimen.
5. Add the same amount of ethanol to the other tube.
6. Observe the contents of both tubes.

Explanation

If the specimen colors the water, then its pigments are water-soluble anthocyanins. Flower petals and strawberries are good examples of these. If the specimen colors the ethanol instead, then its pigments are carotenoids and chlorophyll, which are not water soluble. Carrots and leaves contain these pigments.

Extension activities

Chromatography is a technique used to separate different pigments in a specimen. You can demonstrate the concept by using a felt tip pen with black water-soluble ink to draw a big dot on filter paper. Allow the paper to dry, and then slowly add single drops of water to the dot to see the colors in the black ink separate. For further explorations in chromatography, take a look at the following kits:

• Carolina™ Introduction to Chromatography BioKit®
  Students are introduced to ascending paper chromatography as a method of separating natural biochemicals.
• Fundamentals of Chromatography Kit
  Students learn the techniques of paper and thin-layer chromatography by separating plant pigments from leaf extract.
• The Purloined Parakeet
  Students use chromatography to determine which of a group of pens, isolated from suspects' lockers, was used to write a ransom note for a stolen parakeet.