The Chemistry of the Fall

By: Ali Davidson

Summary

• Autumn is a beautiful time of year for many reasons. The air begins to feel a bit crisper, hot apple cider starts to sound good again, and the leaves of the trees begin to change into many gorgeous colors.

• However, there are very specific reasons due to the chemistry in the leaves that causes this change.

Summary, continued

• Chlorophyll in the leaves begins to receive less and less sunlight, and pigments that are not usually seen begin to come out due to the lack of proper sunlight for the green color to show through (Shakhashiri 1).

• The carotenoids, which produce the “fall colors” such as yellow, orange, and brown in leaves, begin to show through more and more, causing the leaves to change colors (Tackett 1).

Chemistry: The three pigments in leaves

Chlorophyll • Main component of leaves

• Two types:• C55H72MgN4O5 for chlorophyll a

• C55H70MgN4O6 for chlorophyll b

• Produce green coloring in leaves

• Is involved in photosynthesis, which provides food for the plant

• (Lear 8-9)

Carotenoids • Produce brown, orange, and yellow

colors

• Most perceived “fall colors” come from carotenoids

• (Lear 8-9)

Anthocyanin• Produce blue and red

coloring in plants

• (Lear 8-9)

Chemistry: Photosynthesis

• Shakhashiri labels photosynthesis is an endothermic reaction, which we learned as a reaction that gains energy.

• An equation to model photosynthesis could be represented one of two ways:• Shakhashiri uses the equation: xCO2 + xH2O light/chlorophyll Cx (H2O)x +

xO2• Lear uses the equation: 6CO2 + 7H20 + Sunlight Chlorophyll C6H12O6 +

6O2 + H2O. Lear also states that “chlorophyll can be regarded as a catalyst” (8). We learned that a catalyst helps to boost the reaction, without actually getting involved.

• Photosynthesis is how leaves produce sugars to sustain themselves. They use the sunlight and chlorophyll to make sugar (C6H12O6).

Chemistry: Changes in the Fall

• In the fall, trees begin to signal to their leaves to cease production due to the changing weather. Without the necessary sunlight and warmth for photosynthesis, the leaves can no longer sustain themselves, so they have to decompose for the winter.

• The proteins used in photosynthesis break into amino acids, and shut down for the winter.

• When this occurs, the chlorophyll goes through a decomposition reaction. All of the pigments go through decomposition, but the chlorophyll happens to be the fastest, which is why we can see the beautiful yellow, orange, and brown from carotenoids, as well as the bright red from the anthocyanin (Shakhashiri 2).

Implications

• The chemistry of autumn colors matters to us because we can see them everywhere in Nashville from sometime in September to late November.

• Knowing the chemistry of these changes allows us to be able to acknowledge the science behind a beautiful season.

• Next time you see changing leaves, think of chlorophyll and its decomposition.

Works Cited

Lear, Brad. "Autumn Leaves." Chemmatters: 7-10. Print.National Forest Service. USDA Forest Service, 7 July 2011. Web. 3 Apr. 2014. <http://www.na.fs.fed.us/fhp/pubs/leaves/leaves.shtm>.PBS News Hour. PBS, 12 Oct. 2011. Web. 3 Apr. 2014. <http://www.pbs.org/newshour/rundown/why-do-leaves-change-color/>.Shakhashiri. "The Chemistry of Autumn Colors." Scifun. Wics.edu, 23 Jan. 2008. Web. 3 Apr. 2014. <http://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html>.