The Chemistry of Autumn

Every year the leaves of the trees around us change into glorious colors of red, yellow, and orange. After a few weeks of beauty, the leaves float down. We even call this season fall because of the falling leaves. This change in color occurs about the time of the first frosts, so most people assume that Jack Frost causes the striking change. Actually, cool weather does make the colors more vibrant, but the whole process occurs in the chemical factory of the tree.

Chemical Factory Each leaf is a tiny chemical factory. This amazing factory makes food for the tree to use for growth. We still do not understand every part of the process. Here are some things that scientists have discovered. A tree needs several chemicals to make its food. First, a tree needs water, just like we do. The tree sucks up water from the ground to its leaves. It also gets minerals from the soil. Another chemical the tree needs is carbon dioxide, a gas that is in the air. We breathe out carbon dioxide and trees pull carbon dioxide in through tiny holes in the leaves. Of course, trees need sunshine to grow. The leaf colors come from pigments or dyes.

Leaf Pigments A chemical called chlorophyll mixes the water, minerals, and carbon dioxide together and uses energy from the sunshine to make food for the tree. Chlorophyll is a very dark green color, so the leaves get their green from this pigment. The food that the leaves make is a kind of sugar. The tree sends the sugar from the leaves into the trunk where it makes make more wood. Some of the sugar is stored for winter when there are no leaves. This whole process is called photosynthesis.

Summer Leaves In the spring, leaves of trees are light green. As summer approaches, the leaves become darker green. Their work as the chemical factory for the tree has begun. The chlorophyll in the leaves mixes the ingredients and the tree begins using the sugar to grow.

Autumn Leaves In autumn, the tree senses that the days are getting shorter, meaning that winter is coming. A tiny barrier of tissue grows across the twigs that hold each leaf onto the tree. Now the leaf cannot receive any more water and minerals from the soil. The chemical factory starts to slow down and the chlorophyll begins to decompose. The leaves begin to look yellow and orange.

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