Why are plants green

Before we talk about why plants are green, it will be handy to understand why they look green. In order for something to look a particular color it must reflect that color of light to our eyes. In the case of plants, this means they are reflecting only green light and are absorbing the red and blue frequencies of the light spectrum. Since sunlight is made up of more red and blue light than green, this would suggest that plants absorb a lot of sunlight and are somehow optimized for this.

Plants need sunlight for a process known as photosynthesis, which is a method of transforming the light energy they absorb into the energy needed for them to grow, which is why they need to absorb as much light as possible. The chemical responsible for the absorption of light is known as Chlorophyll, and it is the molecules of this chemical that make the plant appear green. Due to a process of evolution, plants have become dominantly green as this is the most optimal color for the absorption of sunlight, which plants need to survive.
The Chlorophyll cells within the plant leaves are perfectly optimized to absorb the red and blue light from the sun because this is the kind of light the plant can make use of in Photosynthesis. The remaining light is reflected back which makes the leaves appear green to our eyes.

Why are Plants not Black?

If plants need to absorb as much light as possible, why do they not make use of all light waves and absorb all the light, causing the plant to appear black visually? This is a question that for the most part remains unanswered. Unfortunately, why the plant does not absorb all light waves is not known however, we do know that the light waves it is missing out on are fairly shallow when compared to the other light waves it does absorb. Plants are actually very efficient at absorbing light and the loss of one light wave is not a problem for the plants.

Imagine an Alien Planet…

One common question in Biology regarding plant life is to imagine an alien planet with a green sun. Would the plant life on that planet still be green? Naturally, through evolution we would expect the plant life to adapt to absorb whatever available light they can so if the main light source is dominantly green, the plant would almost definitely not be green in colour itself. In fact you could imagine the plant would be pink in order to fully absorb the green wavelengths.

A Purple Sun

There are also some theories that when photosynthesis first developed our oceans were purple and our sun was purple. This would explain the absence of a green absorbing Chlorophyll in plants if this were true. It’s also worth noting that some plant do in fact have purple or very dark leaves which would suggest some species of plant do make an effort of absorbing different light waves although green coloured plants remain the most dominant type.