Tuesday, October 14, 2008

15 Minute : Know It : Why Do Leaves Change Color in the Fall?

I lived in Pennsylvania about ten years ago and the first fall I was there, I was shocked by how gorgeous the landscape looked with the changing of the leaves. Everywhere we drove and everywhere we looked it was a riot of jewel-like colors: ruby reds, deep purples, violent oranges, and mustard yellows. It seemed that overnight the entire countryside turned from a green velvet blanket to this wild assortment of lollipop colors.

I think that was when I first really wondered: what makes leaves change their color? And why do they do it every fall?

Well, in order to understand the process you have to be able to explain a few rather large words:

  • Glucose: a kind of sugar. Plants use sunlight to turn carbon dioxide and water into glucose. Glucose is food for plants. So, plants like sugar just as much as your kids do!

  • Photosynthesis: the way plants turn carbon dioxide and water into sugar.

  • Chlorophyll: a chemical that helps with photosynthesis. It also gives plants their green color.

When the days get shorter and cooler in the fall, this signals that trees to begin to get ready for winter. They will rest during winter and live off the food they stored during the summer. They begin to shut down their food-making process, or photosynthesis, and the green chlorophyll disappears from the leaves of trees. When this bright green fades, you can begin to see orange and yellow colors appear. Those colors were always present in the leaves, but during the summer they are covered by the green of the chlorophyll.

The bright reds and purples that appear in the autumn come about because of the glucose in the leaves. Here is an quick explanation:

In some trees, like maples, glucose is trapped in the leaves after
photosynthesis stops. Sunlight and the cool nights of autumn cause the
leaves to turn this glucose into a red color. The brown color of trees like
oaks is made from wastes left in the leaves. (via sciencemadesimple.com)

So, leaves change color because the green chlorophyll departs in the autumn. We get oranges and yellows from this event. When chlorophyll departs, photosynthesis winds down and the glucose in some leaves is turned to red. The changing colors let you know that Nature is beginning her long winter's nap.

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