Why are plants green?

Satellite photos such as the one above depict our precious planetary home as a roughly spherical object colored with some mix of white, blue, green and brown pigments. I’m fairly confident that pretty much all of us know that the white color comes from snow, the blue color comes from bodies of water on our planet, the brown color comes from dirt in various forms, and the prominent green color comes from plants.

To be specific, saying that plants are green is a blanket statement that isn’t entirely accurate because it doesn’t always apply. It is probably more accurate to say that most plants and trees tend to have green leaves. Such consistency from organism to organism within the same species is usually no accident as mother nature tends to be ruthlessly efficient. An analogy to this train of thought would be how most mammals (us, apes, lions, tigers, bears) all have teeth. The important reason for why all of us mammals tend to have teeth is because we need to chew/digest our food in order to stay alive. In the same way, it stands to reason that there is probably an important functional reason for why plants have evolved to have green leaves. Alright, let’s put aside all this “meta-talk” and get down to the business of understanding why plants often have green leaves.

Have you ever stopped to wonder why plant leaves are often green? I mean why not red, or blue, or any of the other colors in the visible light spectrum (Red, Orange, Yellow, Green, Blue, Indigo, Violet) for that matter? The reason why plants have green leaves is because they contain a chemical called chlorophyll. Chlorophyll is derived from the greek words “chloros” which means green, and “phyllon” which means leaf. So in plain english, chlorophyll actually directly translates to “green leaf”. When we isolate chlorophyll in a chemistry laboratory, it has the same strong green color as we see on plant leaves. The scientific reason for this is that while chlorophyll is pretty good at absorbing light from the blue and red ends of the visible light spectrum, it most strongly reflects green light which is why it looks green to the human eye. If you’ve been paying attention, the next question that should have popped into your head at this point is… why do plants need chlorophyll? Good question, let me explain.

You see, plants aren’t like us that can run around and kill random critters and pluck fruits for food… they are pretty much rooted (no pun intended) to roughly the same spot for the entirety of their natural lives assuming we humans don’t interfere. As a result, plants have evolved to feed themselves with things that they don’t have to move around too drastically to gain access to such as sunlight, carbon dioxide (CO₂), water (H₂O), and soil. Of all those resources mentioned above, the one that most baffled me as a youngster was sunlight because I didn’t think of it as a tangible thing like soil or water that you can store in a glass jar for example. That being said, nature has invented an ingenious way for plants to feed themselves using sunlight, and most of that magical process is due in large part to the chemical called chlorophyll.

To cut a long story short so that you can get the gist of it without getting lost in a maze of scientific jargon, chlorophyll has the ability to absorb sunlight and use it as a source of energy to kickstart a chemical reaction within the plant that combines CO₂ and water to form sugars that serve as nutrition for the plant. This process is called photosynthesis which loosely translates to “using light to make stuff”. The “stuff” that comes about through photosynthesis is nutrition for the plants, and an important byproduct which a lot of the other living things on earth need to survive.

Photosynthesis is a truly remarkable process because it uses two inert substances – water and carbon dioxide – to make food for the plant, releasing a byproduct called oxygen (O₂). Yup… oxygen is that ubiquitous gas that pretty much all living animals need to breathe in order to stay alive. That to me shows the power of nature. Here we are in all our technological brilliance still burning fossil fuels to make energy, and steadily destroying our environment as a consequence. Meanwhile, nature in her infinite wisdom has figured out a way to use sunlight to sustain plants while at the same time making those same plants a source of oxygen and nutrition for us. In a word, amazing. So the next time you walk by a tree, be grateful. It has probably spent decades to centuries steadily producing oxygen for us to breathe while doing very little damage to our magnificent planet. Till next time folks, take care of yourselves and each other.

Without Wax
Oyolu B.C. Ph.D.
chubaoyolu.org
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