Why Do Leaves Change Color in the Fall?

Well, in fact, the leaves don’t change color! Each year, throughout New England, Colorado, Wisconsin, and many northern areas of the country, autumn is a beautiful time to appreciate the wonders of Mother Nature. This year, the colors were especially breathtaking in New England due to a drought and some mild weather. But wait…do they really change colors? Here’s the science story behind this incredible phenomenon:

It’s all about photosynthesis. You see, leaves are “food factories”, and photosynthesis is the process of making and storing food. Chlorophyll is the green chemical that helps convert sunlight to food (sugars). In autumn, the tree prepares for winter by moving chemicals from the leaves to the branches and trunk, and eventually, down to the roots. This is signaled by shorter days and cooler nights. The chemicals include nitrogen compounds, potassium, and phosphorus. These moving chemicals cause the green chlorophyll in the leaves to decompose. Left behind are carotenes (yellow, orange, and brown) and anthocyanins (red and purple) that have been in the leaves all year, but weren’t seen because of all of the green chlorophyll. So, you see, they don’t change color, they just lose the green chlorophyll, exposing the other pigments (carotenes and anthocyanins).

Weather is a factor, and some years are more colorful than others. The fall weather conditions that produce the most vibrant colors are sunny days, followed by cool, dry nights. This is because leaves manufacture sugars during the warm daylight hours, but the cool nights prevent the sugar from moving from the leaves. This helps to produce more anthocyanin ( the red pigment), resulting in more colorful leaves. This is why some trees will be very red on the sunny side of the tree, while the shadier side is yellower. Interestingly, frost is NOT required for autumn colors.

Want to learn more and have fun at the same time? Check out the Photosynthesis Song, one of many songs on my Sing Along Science CD’s. The songs are also available on ITunes, and they’ll help your students remember facts for a lifetime! Enjoy the Season!

Scientifically Yours,

Warren G. Phillips

 

You can see my bio at http://en.wikipedia.org/wiki/Warren_G._Phillips

Please see www.singalongscience.com for more information.