Plants are green because they are made of chlorophyll. Chlorophyll absorbs light on the opposite ends of the electromagnetic spectrum (blue and red), but is poor at absorbing light in the green range of the spectrum. This is the basic reason why plants are green.
Chlorophyll Makes Plants Look Green
Within the cells of plants are little green structures called chloroplasts. Inside chloroplasts is where photosynthesis takes place; the process by which plants make energy. Inside chloroplasts are the chlorophyll molecules that do the brunt of the work.
Chlorophyll molecules are grouped into larger systems, called photo systems, which are part of a larger system called chloroplasts. By capturing light from the blue and red spectrum (aka ultraviolet and infrared), chlorophyll molecules take that energy and transfer it to a pair of special receptors within their photo system.
When chlorophyll captures a photon of light, a chain reaction of events takes place which eventually forms the chemical energy used by plants. This chain reaction is called photosynthesis.
Why Chlorophyll Absorbs Red and Blue Light
The reason the ultraviolet and infrared light is absorbed is photosynthesis. Photons are just a bundle of light energy. From the sun, or a light source like a UV lamp, photons are emitted. When a photon within the ultraviolet or infrared range of comes into contact with chlorophyll, the electrons in the chlorophyll will be raised to a higher energy level. “Higher energy level” is a physics term relating to the energy of the electron or of molecules themselves.
When the electron begins to return to its original “non-high” state, the excess energy is transferred to nearby molecules and is repeated via various electron acceptors. During this process, the chloroplast also begins to work by creating protons, resulting in the synthetic creation of Adenosine-5'-triphosphate, or ATP. This ATP is the how the energy is chemically transferred to various other cells of the plant, to be used as metabolism.
So, because visible light in the green spectrum is not absorbed so much and isn’t used by the chlorophyll, the plant looks green. Light in the green spectrum of light is reflected back. Some plants have different pigments other than chlorophyll. Carotene, which makes carrots look orange, is an example of this.
What is Green?
The deeper, underlying philosophical question is, “Why is there green at all?” The answer lies within human biology and how humans perceive color. The eye is a receptor of light, and the light image that is captured by the eyes is transferred to the brain, which interprets the image being seen.
The colors that humans see are how the brain interprets the different wave lengths of the electromagnetic spectrum of light. Green is the perception of light within the spectrum of light wavelengths of 520–570 nanometres.
In other words, green is really an arbitrary color, and is apparently manufactured by the human brain, in order to perceive wavelengths of light.
Sources
- Speer, Brian R. (1997). "Photosynthetic Pigments" in UCMP Glossary (online). University of California, Berkeley Museum of Paleontology. Verified availability March 12, 2007.
- "Human Vision and Color Perception". Olympus Microscopy Resource Center. http://www.olympusmicro.com/primer/lightandcolor/humanvisionintro.html. Retrieved 2007-09-19
Andrew Perry - Andrew has a B.A. in Philosophy & Journalism. He has worked professionally for newspapers, news sites, and local government.
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