The Chemistry of Leaves Changing Color

Introduction

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Leaves that grow on trees have many different colors they can change into in the fall.  Each color has its own unique chemical compound that will decide what color the leaf will change into.

I chose to find out how leaves change color because it has always fascinated me wondering why and how this this takes place.  Everyone can find a little joy in finding a nice park with beautiful leaves in their fall colors to go for a walk and clear your head.  Fall colors are also very popular with photographers because they make for great shots.


Composition of ...

Chlorophyll

which gives leaves their basic green color.

Formula: C55H72O5N4Mg

Carotenoids

which produce yellow, orange, and brown colors in such things as corn, carrots, and daffodils, and bananas.

Formula: C40H56

Anthocyanins

which give color to such familiar things as cranberries, red apples, blueberries, cherries, strawberries, and plums.

Formula: C15H11O+



Main Chemicals, Compounds, Components

Chlorophyll

Naturally occurring that gives the leaves its normal green color. Green pigment absorbing rays from the sun. Green color during the spring and summer while the leaves are young. It absorbs sunlight helping the process of photosynthesis to create energy. This process occurs within the leaf .

Carotenoids

Naturally occurring that gives the leaves its yellow-orange color. Orange pigment occurring from absorbing certain color of sun rays. Occurs in the fall when the trees have to begin the process of shedding their leaves for survival. So the tree can shed to survive the cold winter. Occurs within the leaf and begins to sever the connection between the leaf and the tree.

Anthocyanins

Naturally occurring that gives the leaves its red color. Red pigment occurring by absorbing certain colors of sun rays. Occurs in the fall when the trees have to begin the process of shedding their leaves for survival. Enable the tree to shed its leaves to survive the winter. Occurs within the leaf and begins to sever the connection between the leaf and the tree.


Chemistry's Role

The color components in leaves are all natural.  Every leaf that is grown has these chemical components in them.  The final product of these chemicals is the color of each fall leaf you see in the tree.  As the chlorophyll breaks down these chemicals take over the color of the leaf.      Green pigment in leaves is chlorophyll it absorbs red and blue light from the sun.  The light reflected by the leaf is diminished in red and blue to green.  Chlorophyll is a very unstable compound. The reaction to make chlorophyll is so unusual it involves a covalent intermediate in which glutamic acid is attached to a RNA molecule.

Another pigment found in leaves is carotene. It absorbs blue-green and blue light making the color of the leaf yellow. Contained in the chloroplasts of many plants. It is a substance that inhibits  the oxidation of other molecules.

A third pigment in a leaf is anthocyanins. They absorb blue, blue-green, and green light.  The color produced by these is Red. Not all trees produce anthocyanins because it is a very complicated process to create the compound.


Background Research

Everyone loves the beautiful Autumn colors. All of the colors, the red, purple, orange, and yellows are all results of a chemical process.  During Summer and Spring leaves serve as foods necessary for the trees growth.  Along with the green pigment are yellow to orange pigments, carotenes and xanthophyll pigments. An example is the orange color it gives to a carrot. Most of the year these colors are masked by great amounts of green coloring.

In the fall because of the changes in daylight and the changes in temperature, the leaves quit making food.  The chlorophyll breaks down and the green pigments go away. As the fall colors appear other things take place within the leaf.  The point where the stem meets the tree a layer of cells begin to appear slowly severing the tissue that supports the leaf.  The tree seals the cut until the leaf is finally blown off and leaves behind a leaf scar on the tree. Temperature, light, and color have an effect on how long the fall colors last. Low temperatures will have a higher chance to form bright red leaves.  Rainy and overcast tend to influence the intensity of the fall colors.  Colors of the leaves also vary due to the species of tree they are on.

Evergreen trees are able to survive winter because they contain a heavy wax coating fluid inside their cells that contains substances that resist freezing.  Thus the foliage can survive the most severe weather conditions including those of the arctic.  Evergreen needles can survive for many years before falling off because of old age.  On the other hand the leaves of broad-leafed plants are very easily damaged.  The leaves are typically broad and thin not protected by any thick coverings.  These leaves contain a very watery sap that freezes quickly.  The cells would have no chance of surviving the winter.Tissues of leaves that are unable to survive the winter must be sealed and shed to ensure the plants best chance of survival.  That is why leaves fall every pre-winter.

People love the color of fall leaves.  But what happens to the leaves when they fall off the tree?  They decompose and stock the soil with rich nutrients.They make up a humus layer that absorbs and holds rainfall. It also becomes food for many various soil organisms.  The forest could very well not survive without the annual replenishment of leaves.

Many people think the cold weather of the frost is what causes the leaves color to change.  Temperature will dictate the strength of the color that comes but is only one of many environmental factors.  The temperature, precipitation, and light are the factors that come into deciding the brightness of color but the reason the leaves fall is due to the trees need to survive.


Resources

http://chemistry.about.com/od/howthingsworkfaqs/f/fallleafcolor.htm

  • If leaves are a certain color they contain which compound

  • Chart of leaf pigments and their colors

  • What surrounding conditions affect the color of the leaves

http://www.compoundchem.com/2014/09/11/autumnleaves/

  • Chemistry of colors of fall leaves

  • Explains how each compound changes the color

  • Picture of each molecule

  • Which compound makes which color

http://io9.gizmodo.com/5849745/the-chemical-reaction-that-causes-leaves-to-change-color-in-fall

  • Chemicals that cause leaves to change color

  • How each color appears to the eye

  • Decomposition of chlorophyll

  • Contributing factors of the colors changing

https://www.na.fs.fed.us/fhp/pubs/leaves/leaves.shtm

  • Evergreen leaves/pine needles

  • Broad-leafed plant leaves

  • What happens to leaves when they fall off

  • Climate effects on leaves

http://www.esf.edu/pubprog/brochure/leaves/leaves.htm

  • Colors of leaves

  • Leaves uses (food)

  • What pigments give them their color

  • Why there are different colors

  • Climate effects on leaves colors

http://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html

  • Chlorophyll Molecule

  • Why leaves are green and what colors are absorbed by chlorophyll

About the Author

Tyler Frieders is a Junior at Billings Senior High.  He has always wondered how and why the leaves change color in the fall before they fall off and regrow in the spring.  He plays baseball for the Royals and hopes to continue playing in college.









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