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What Makes Plants Green? Get Your Chlorophyll

Written by Jesse Richardson on April 25, 2011 with 1 Comment

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Green ForestEver wonder what makes plants green? Me too. Although most people pick it up in chemistry class in high school, I needed some refreshing. Then, a friend reminded me of Chlorophyll, the molecule that harnesses the power of sunlight to synthesize carbohydrates from CO2 and water.

It all started coming back.

From Photosynthesis to Chlorophyll – The Journey to Find the Magic Molecule

As described by Paul May, chemist at the University of Bristol, photosynthesis was first discovered English chemist Joseph Priestly. According to Priestly, plants seemed to “restore air which has been injured by the burning of candles…the air would neither extinguish a candle, nor was it all inconvenient to a mouse which I put into it.”

In essence, Priestly discovered that plants produced oxygen.

Soon after, Dutchman Jan Ingenhousz discovered that light plays an essential role in “restoring” the air. Igenhousz recorded, “I observed that plants not only have the faculty to correct bad air… [but] that this wonderful operation is by no means owing to the vegetation of the plant, but to the influence of light of the sun upon the plant.”

All the pieces started falling into place. Plants breathe in CO2 and exhale oxygen. To do this, they use the energy of sunlight, as described above. Originally, chemists assumed chlorophyll was a single compound, but as time went on and technology allowed a closer look, it was discover that chlorophyll’s composition was of a central ion of magnesium and four nitrogen molecules.

While we know that this molecule absorbs the sunlight, we should also know that to do its job of synthesizing proteins, it must be attached to a complication protein. As explained by May, “This protein may look haphazard in design, but it has exactly the correct structure to orient the chlorophyll molecules in the optimal position to enable them to react with nearby CO2 and H2O molecules in a very efficient manner. Several chlorophyll molecules are lurking inside this bacterial photoreceptor protein.”

As the light hits the receptor, electrons are excited. Likewise, an assembly of chemicals come together to dictate the color – most plants are “greened” by the cholorophyll, but others become red, like marine red algae.

As explained by GardenGuides.com, “These chemicals are the porphyrin ring, the chelated magnesium molecule, the hydrocarbon tail, the carotenes and the xanthophylls. Chlorophyll has a green color because it absorbs red and blue-violet light, leaving only a green hue visible.” In the cases of marine algae, however, plants may become red.

Significance of Green

Today, the idea of “green” defines part of the environmental movement. People are urged to undertake acts of green, to support green products, and to find solace in our natural, green surroundings. Corporations have even taken notice, and now engage in the enviro-crime of “greenwashing.” Nevertheless, while the color has new meaning and invokes a range of feeling, it remains as a basic result of organic chemistry.

At the same time, that simple, natural process is helping us to understand how to cleanse our planet. Many engage in carbon offsetting or planting trees precisely for the result Priestly famously observed: the restoring of air.

That said, next time you glance down at the grass or up at the trees, consider just how complex the world really is. There’s a whole lot going on with green.

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