Fall is leaving
This story appeared on page 4 of the Columbia Missourian's
Mini-MO newspaper for kids on October 7, 1996.
By Sid Perkins
Missourian Staff Writer
Well, kids, fall has arrived. The air is turning cool, and the leaves already have begun to change colors and drop from some of the trees.
Did you ever wonder why leaves change colors in the fall, or how it happens? Here's a quick explanation.
First of all, you've probably noticed that not all trees lose their leaves. If you've noticed this, you've got a good eye. There are two major types of trees: deciduous (DEE-SID-JU-US) trees and evergreens. Evergreens keep their leaves and stay green all year long. The deciduous trees are the ones that lose their leaves each year.
In the fall, the days begin to get shorter. The sun is also lower in the sky at noon, which causes temperatures to be cooler. The combination of less sunshine and lower temperatures is what causes the deciduous trees to drop their leaves. In the winter, deciduous trees "go to sleep," sort of like a bear goes into hibernation.
Leaves are the food factories for a plant. Animals have to eat other things for food (including plants and other animals), but plants are special because they can take energy directly from the sun and make their own food. Plants do this by using a chemical in their leaves called chlorophyll (KLOR-O-FILL).
Chlorophyll is green. During the spring and summer the leaves of a deciduous tree look green because there is a lot of chlorophyll there. When the fall comes, however, the sunshine becomes more scarce and the leaves on the trees stop making new chlorophyll. As the old chlorophyll starts to break down, the green color of the leaf begins to go away.
You've probably also noticed that different kinds of trees change different colors. The leaves of some trees turn yellow or orange, while the leaves of other trees turn bright red or purple. The different colors are caused by the different chemical reactions that are happening in the leaves.
For example, the leaves of hickory and birch trees turn yellow when the chlorophyll breaks down. When the green chlorophyll goes away, a yellow pigment in the leaf becomes visible. The yellow pigment was already there during the summer, but it was not easily seen because there was too much green chlorophyll.
Think of it this way: Imagine that you have a fish tank with three yellow fish and 50 green fish. If you stand across the room and look at the fish tank, it will be hard to see the yellow fish. But if all 50 of the green fish are removed from the tank, then you can see the three yellow fish easily.
The pigment that gives a hickory leaf its yellow color is called a carotenoid (KA-ROT-IN-OYD). This is the same type of chemical that makes a squash look yellow and gives carrots their orange color.
In other trees where the leaves turn red or purple, such as red oak and sugar maple trees, a different chemical reaction takes place. In those leaves the chlorophyll also breaks down, but another chemical reaction takes place at the same time. Chemicals, called starches, in the leaves begin to change into chemicals called anthocyanins (ANN-THO-SIGH-ANN-INZ), which give the leaves their red and purple colors.
The best time to see bright fall colors in mid-Missouri is in the middle of October, or late October, depending on the weather in the early fall. If the weather is cool (but not freezing) and there is only a small amount of rain, the bright fall sunshine encourages more chemical reactions to take place in the leaves. This makes the colors of the leaves brighter.
So now you know how and why the leaves of deciduous trees change color in the fall. While you are outside enjoying all of the fall colors, you can feel good that you know a little of the science that explains one of nature's most beautiful sights.
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Copyright 1996 by Missourian Publishing Association Inc.
All rights reserved.
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