Friday, October 26, 2007

a science lesson: Why do leaves change color?

I have been thinking about this question a lot in the past few weeks. As I have previously mentioned, I have never lived in a place that has a real autumn season, with leaves changing color and falling. I'm sure there are some trees where I used to live that do this, but not enough to ever make an impact on my memory. So I have been fascinated by the hundreds of trees that are changing around me here in my new home.

I guess I thought that a tree's leaves all changed color at the same time, but I have noticed that this is not the case. It seems that the leaves that recieve the most sunlight change color first, but why? And why are there so many different colors? Most trees have leaves that are some shade of green, so why do they change to a miriad of different colors- red, orange, yellow...?
I decided to research these questions and was suprised to find that there are not any easy answers. In fact, I was a bit confused at times. This is the simple explanation I came up-

  • All leaves contain chlorophyll (green color) and carotenoids (yellow and orange color). Cholorophyll is necessary for photosynthesis (conversion of carbon dioxide and water to oxygen and sugar).
  • When the days become shorter and there is less light available for photosynthesis, trees start to conserve energy by decreasing the rate of cholorophyll production in the leaves (keeping it from doing photosynthesis, basically killing it). This makes them turn from green to yellow, orange.
  • The red color in leaves is sugar that was made inside of the leaf by photosynthesis but then trapped there because the cold weather closed the leaf's veins and made it unable to send the sugar into the tree. That's why the leaves on the outer part of a tree's canopy turn color first, because they get more sunlight but then get colder and "die" faster that the leaves that are protected inside the canopy.
Probably more than I ever wanted to know about botany, but at least I got my questions answered. I felt like I was the only one living in this area who didn't know why leaves change colors, as if those people who have lived through the autumn season their entire lives just knew. But after reading through all of the explanations and stuff I found on the internet, I realized that most people probably don't.


Walt & Jean said...

Thanks for a very understandable explanation of something I've taken for granted but enjoyed my entire life. I'm so glad you all get to observe this wonder first hand.

Did you get my little package with the fall/Halloween crafts yet? Let me know if you have any questions and if those cute kids liked them.

Love, Jean

Bridgette said...

Very informative and interesting. I'm glad you got to see the trees change color.