Why Do Leaves Change Color in the Fall?
Leaf Science for Preschool and Elementary School Classes
Sep 12, 2009
Fall is a time of change. Animals and plants are both completing their life cycles. The seeds of plants ripen and fall to the ground, waiting for a new year to begin. Deciduous trees lose their leaves as well, and the leaves fall to the ground, providing nutrients for decomposers. These leaves gradually turn into soil and provide nutrients for the new plants that grow in the spring. In the fall, a deciduous forest is a miracle of yellow, orange, and red.
This fall, use a local forest or street trees as an experimental forest. Take a preschool class, daycare, or elementary school class outside to discover and track the changes in autumn leaves.
Why are Leaves Green?
Leaves contain a green substance called chlorophyll. To make food, a plant uses water from the ground and carbon dioxide from the air. Chlorophyll helps photosynthesis happen – it helps plants change water and carbon dioxide into sugar. This sugar is the food that helps plants grow.
Experiment with the green in leaves. Do leaves turn green in the absence of light? Grow the same species of seed in a drawer and on a sunny ledge. Watch to see if there are any differences between the two seedlings. Pea and bean seeds are particularly good candidates for this experiment, since they grow quickly.
Why Do Leaves Change Color in the Fall?
In the fall, the days get shorter. This tells the plants that it will soon be winter. In the winter there is not a lot of sunlight, so deciduous trees begin to stop making food. The chlorophyll fades. Inside a leaf there are many pigments, but during the growing season these pigments are obscured by the green of the chlorophyll. When the leaves begin to stop making food, the other pigments become evident in the leaf.
Discover the different colors in fall leaves. Go on a leaf walk and collect different colors of leaves. Investigate the leaves. Ask questions such as:
- What color patterns are visible?
- Are there more green leaves on trees in a specific area of the street or the forest?
- Are there more green leaves on plants that live in the shady understory of the forest?
Draw the leaves for a scrapbook. Make a note about where the students found particular leaves.
Why are Different Leaves Different Colors in the Fall?
Different tree species have different leaf colors. Most of the leaf colors are present in the leaves all year. Carotenoids produce yellow, orange and brown. The red and purple colors that are present in the leaves are made in the fall. They are made from the sugar in the leaf cells.
Use field guides to classify the leaves that the students have found. The class can:
- Press the leaves
- Take rubbings of them to preserve them.
- Classify the leaves by species
- Sort the leaves by color
Do different tree species have different colors of fall leaves?
Why Do Some Trees Lose Their Leaves?
Some trees have leaves that are very sturdy and waxy. These are called needles. Needles are protected against the challenges of the winter weather because they are small, thick, contain antifreeze, and retain moisture easily. Large, thin leaves are not as well protected, so when fall comes the tree discards these leaves. The trees that lose their leaves are called deciduous trees.
Experiment with a deciduous and coniferous tree. Use tree seedlings to experiment. Place one deciduous and coniferous tree in a cool place and the other on a warm shelf. Compare the growth of the trees.
Exploring fall leaves is a natural part of any preschool or elementary school science unit in the fall. With very little equipment, preschool and elementary school students can learn about chlorophyll, leaf pigments, and the changes that happen to different trees in the fall. Whether it involves a trip down the block or to a nearby forest, leaf science is an easy and fun autumn science unit.
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