Fall is Coming – Science Behind Leaf Colors

To many, the bright yellows, oranges, and deep reds and purples of fall are a mystery they’d rather just stare in wonderment at. To the infinitely curious, they often wonder how and why the fall leaves change colors, and sometimes with more magnificent displays than in previous years. The science behind leaf colors can be a bit complicated – but today, we’ll try to simplify the process.

It All Starts With Photosynthesis

The biggest job of trees is photosynthesis, or turning water, light, and carbon dioxide into sugars and oxygen. The process of photosynthesis requires a special pigment, chlorophyll, or what is known for giving leaves of deciduous tree their summary green hue. In the summer, Photosynthesis is happening rapidly, and the leaves contain more chlorophyll than any other pigments because it is necessary to keep photosynthesis occurring. A little known fact is that green leaves actually already contain the fall pigments (orange, yellow, red, and purple), they are just being overrun by the amount of chlorophyll during the busiest months for photosynthesis. All deciduous leaves also need two other pigments, carotenoids and anthocyanins for photosynthesis. Carotenoids are yellow and orange, and provide the color to things like pumpkins, sweet potatoes and carrots. Anthocyanins give color to stuff like berries, red cabbage, and cherries. When photosynthesis slows down in the fall, chlorophyll leaves the leaves and reveals the carotenoids and anthocyanins underneath. So perhaps using the word “change” is not really accurate, maybe a better word would be that the leaves are “revealing” their colors.

Bonus Fact: The word “deciduous” is Latin and means “to fall off”.

Need something a bit more visual to help you understand? Check out this Sci Show video which gives a great explanation of the process.

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