Originally printed in the Oct. 30, 2002 edition of the Illinois Valley News
Fall is one of my favorite seasons of the year. Especially the cooler days, I look forward to them all summer. Even the rain usually has a welcome sound and calming effect on the area. Colors in the fall are an extra side benefit, considering the alternative of having all year be the same.
During the summer, green is the dominant color of the woods with a few spots of blossoms which temporarily appear before green comes back in control. Since trees do not produce their own light, the color we see is a reflection of sunlight. Energy from the sun is made of many different wavelengths of light which all blended together produce white. Prisms and rainbows show the separate colors which make up sunlight.
Chlorophyll is the pigment which makes plants green. Chlorophyll is a very complex molecule with many carbon and hydrogen atoms and a magnesium atom in the center. Two other big animal molecules have an almost identical structure. Hemoglobin in blood with an iron molecule in its center and vitamin B 12 has cobalt where magnesium is located in chlorophyll. Chlorophyll is green because it has absorbed all the other colors of light and only reflects wavelengths that produce the color green.
The energy of the absorbed wavelengths is used by the leaf cells in the process of photosynthesis. The first step in the process is to use the absorbed energy to separate water molecules, H2O, into hydrogen and oxygen atoms. The oxygen is released back into the air as a waste material for animals to use. The hydrogen is combined with carbon dioxide from the air, in a complex series of steps, to produce a simple sugar called glucose. Glucose is then converted by the plant’s chemical processes into carbohydrates, as well as protein and even more chlorophyll.
Making more chlorophyll is critical because it gets used up quickly during photosynthesis and has to be constantly replenished. This brings me back to fall colors because many plants stop producing chlorophyll in the fall. This is the first step in order to shut down for the winter and become dormant. When this happens, the other colors, which were covered up all summer, begin to be visible as the chlorophyll becomes depleted. The red, orange, and yellow pigments then become the dominant color. During the summer they also absorbed wavelengths of light, though different than what chlorophyll absorbed, which added to the efficiency of photosynthesis. These other pigments also help protect the plant from ultraviolet energy in sunlight.
The yellow and orange pigments, called carotenes, are abundant in carrots and pumpkins and also in many fall leaves such as birch and Big Leaf Maple trees. The red pigment, called anthocyanin is found in the cell sap and changes color with the sugar content. This is what makes apples red, grapes purple and also turns dogwood and poison oak leaves red in the fall.
Chlorophyll and the other pigments are essential to almost all living things on the earth. Plants convert sunlight energy into food energy which all animals, including humans require. Photosynthesis is at the beginning of nearly all land and marine food chains.