Sunday rerun: I think it's time we leave

Every year at about this time, I get the same question from friends and family.  It's always a variation on the same theme, but the question boils down to, "What the hell is the matter with you, anyway?"

No, just kidding.  You know I get that question all year long.  The question that pops up as the nights grow longer and people start looking around for the blankets and quilts they put away in May is, how come the leaves change color every year?

And I thought I ought to look it up, because until I just did, I would have to tell people to ask my friend Mr Damifeyeno.

I got this scoop from www.sciencemadesimple.com and, as with all things scientific, it wasn't quite simple enough the first time I read it, but after a couple of passes, it cleared up somewhat.

Here 'tis...

All spring and summer, plants (which trees are, after all) take water out of the ground through their roots, and they take carbon dioxide through the air. Through photosynthesis, the process we were supposed to learn about in high school science while we were trying to figure out how to get a date with the girl at the next bunsen burner, the trees use sunlight to turn water and carbon dioxide into oxygen and glucose. Like Jumpin Jack Flash, Oxygen is a gas gas gas in the air that we breathe.  Plants use their glucose as food for energy and for growing, as they are not able to shop for food on their own, and very few pizza places will deliver to "The Third Elm on Maple Street."  Chlorophyll is involved in this photosynthesis, and it's chlorophyll, along with envy, that turns plants green.

When autumn is on its way, days get shorter, and the trees get less sunshine, so they figure it's time to put on the winter clothes.  Meanwhile, we have people driving cars and owning property who can't figure out that it's not tank top weather anymore.

Photosynthesis takes off all winter, without light or water to operate, so trees live off the glucose they put in their little wooden pantries all summer long and stop preparing food. Well, there goes the chlorophyll!  And the leaves become yellow and orange.  It's not so much that the leaves turn yellow and orange; they lose the green when photosynthesis ends, and with the green pigmentation that used to cover up the golden colors no longer there anymore, we get what we get.

Red leaves, such as on maple trees, occur because glucose is trapped in the leaves when photosynthesis stops, and a combination of sun and cool nights turn the leaves red, just as reading The SUN on a cool night makes Robert Ehrlich turn red. For the same kind of reason, oak leaves turn brown from what's left in them when photosynthesis ends. We just don't know why a tree with like 200 leaves on it will drop 200,000 leaves to be raked up.

And that's what I got from the article.  I hope it sheds some light on the amazing natural process known as the changing colors of leaves in autumn.  Next week here on Science Corner with Uncle Mark, let's try to figure out whatever happened to Axl Rose.