Thursday, September 25, 2008

Why do leaves change color?

"Why do leaves change color in autumn?"

Oh, good, an easier one. :)

Green plants use a chemical called chlorophyll to absorb sunlight, which is needed to metabolize carbon dioxide and water into the sugars the plants need to grow. The carbon dioxide is absorbed from the air (through the leaves, via a process called respiration), and the water is absorbed through the ground.

When fall comes, the days get shorter (less sunlight), which signals the plants to stop producing so much chlorophyll. The plants need to produce less chlorophyll because there's less sunlight and because the winter is generally drier than the rest of the year. So, because there's less sunlight and less water, the plants basically go into hibernation (wrong word, of course) until the days become longer, warmer, and wetter.

Because the plants are not producing chlorophyll, the green color of the leaves fades and the less dominant colors come out. Those colors were there all along, of course, but they were overwhelmed by the green from the chlorophyll.


Kerry said...

I feel like you need more comments on your blog, so I'm commenting; that's very interesting about the leaves. Thank you for the informative answer. : )

Grumpator said...

I will support Kerry in commenting on your blog. I was thinking about why not as many leaves change color in Phoenix, because of course, even though it's warm, the days are just as short. Fortunately, my acute librarian brain remembered that the trees that survive best in Phoenix are not deciduous - hence, they act differently. Our poor little oak tree will be shedding its leaves soon.