As the Fall season approaches, temperatures become cooler, the smell of bonfires fill the air and crispy leaves change colors as they fall from the trees. Because of this, fall brings a sense of new beginnings, warmth and comfort, but it also brings a lot of chemistry. None of the changes in the air, leaves or temperatures would happen if it weren’t for chemistry.
We all learned about photosynthesis long ago, but what about the other roles that chemistry plays within the season? Chemistry is found all around us during fall.
The magic of fall goes far beyond our eyes – it’s a world of science. Pigments reflect certain wavelengths of light, and during the fall certain pigments such as yellow and orange are more visible than others like green. This allows us to see fall leaves as the color they are.
During the warmer summer months, the brightest pigment in plant leaves is chlorophyll, better known as green. Some other pigments, like in yellow, are carotenoids. This is what gives us beautiful summer green yards and leaves. Interestingly enough, the leaves changing colors in hues of reds, browns and golden yellows is due to the chemical reactions to the temperatures and sunlight.
In northern states, depending on certain tree species, leaves can be found in reds and purples. These pigments are called anthocyanins and develop in late summer and fall. These hues are due to the stress from outside temperature changes such as when it snows. The shades of red are all determined by how anthocyanins mixes with other factors as in the acidity, mineral count and leaf cells.
Additionally, with fall comes shorter sunlit days and cooler temperatures, which also help the color change in leaves. When the leaves change colors, we take it as a sign of fall, but it’s also chemistry working at its best. Seasons shift and chlorophyll levels drop, which signals the release of hormones. Ethylene and Auxin are the two plant hormones which create this change. Ethylene is a gas produced from methionine, an amino acid, which accelerates fruit maturation but decreases leaf growth. This combination of gas and biosynthesis is what causes the leaves to fall.
Now get to work raking up all those leaves!