Sunday, November 4, 2012

So you slept through science class, part 4–Why do the leaves change color in the fall?

It’s one of the most beautiful times of year – the leaves are turning spectacular colors (especially if you live in New England) and there’s a little chill in the air.  So the environmental science question of the day is one that you might know the answer to, or maybe your kids asked you and you didn’t know the answer:  Why do the leaves change color in the fall?  If you’d like to give a better answer than, “the trees are going to sleep for the winter,”  it’s pretty simple if you remember a few little facts.

  • Leaves, like all living matter, are made up of cells.  Cells are made of molecules.
  • Inside of the cells of leaves are pigment molecules that capture light energy to turn into food for the tree.
  • Different pigments capture different wavelengths of light.
  • The pigment molecule that gives trees their green color is called “chlorophyll.”  But there are other pigment molecules helping to trap other wavelengths of light – we just don’t see them, because they’re dominated by chlorophyll.
  • Trees have to actively produce chlorophyll throughout the growing season; this production takes energy.
  • As day length decreases in the fall, trees stop making chlorophyll (it’s kind of the tree’s own cost/benefit analysis).  The molecule breaks down and the other pigments that have been in the leaves all along become visible!

Want a more detailed explanation of our fall foliage fireworks?  Check out this great U.S. Forest Service website!

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