How does light color affect photosynthesis?

Written by angie chipera
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How does light color affect photosynthesis?
Plant leaves absorbing light (Green Plant image by Starlyn from Fotolia.com)

Photosynthesis comes from the Greek words "light" and "putting together." During photosynthesis, plants absorb light energy and use it to make molecules of adenosine triphosphate (ATP). ATP is the building block for plants in much the same way as DNA is for humans.

Researchers have shown that plants subjected to certain shades of colour rather than the entire spectrum have varying degrees of growth.

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Light

Light travels in waves but also as little energy packets called photons. A photon of light contains the entire visible spectrum: red, orange, yellow, green, blue, indigo and violet. Plants absorb red, orange, yellow, blue, indigo and violet wavelengths of light but reflect green. When wavelengths of light are absorbed, they are no longer available for eyes to see, which is why plants look green.

How does light color affect photosynthesis?
Visible light broken down into a light spectrum (rainbow-coloured abstract blurry background image by garloon from Fotolia.com)

Pigments

Pigments absorb light. The pigment chlorophyll, found in green plants, absorbs violet, blue and red wavelengths. Carotenoids absorb red, orange and yellow wavelengths, while phycobilins absorb red and blue wavelengths.

Photosynthesis

During the process of photosynthesis, pigments absorb light and convert it to energy. The energy, along with carbon dioxide and water, is used to make sugar. This sugar molecule bonds with the adenine, a colourless crystalline substance, and three phosphate groups to form the molecule adenosine triphosphate (ATP).

Carbon dioxide exists in the air just like oxygen. It's true that plants use carbon dioxide and give off oxygen as a waste product. During photosynthesis, six molecules of carbon dioxide plus six molecules of water plus the light energy yields a molecule of sugar and six molecules of oxygen. The carbon dioxide is broken into its two elements, carbon and oxygen, and water into its component parts, hydrogen and oxygen. The elements carbon and hydrogen recombine with some of the oxygen to form sugar, which the plant uses to grow. The rest of the oxygen is excreted into the air.

Limited Light Spectra

Plants grow best when exposed to the entire visible light spectrum. Scientists experimenting with different colours of light agree that exposing plants to limited light spectra alters the process of photosynthesis. Indoor-plant growers use blue light, because plants exposed to blue light grow better than plants exposed to other wavelengths. Red comes in second and yellow, third. Plants grow badly in green light, which make sense, since green light is the colour reflected by plants.

Other Light Phenomenon

Plants with little light exposure grew taller because they are trying to reach the sun. They are also pale in colour but change back to green when exposed to more light.

Plants living deep in the ocean aren't exposed to enough sunlight to produce the sugar they need for food. Instead of photosynthesis, they use chemosynthesis. They obtain their energy from sulphates, nitrites, iron compounds and other substances.

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