Why are plants green and not another color?

Answer 1

Botanists have been asking this question for ages. We know plants are green because they reflect the green light, and absorb the red and blue light from the visible light spectrum to use in photosynthesis, or the process of turning light energy to something the plant can use. Why don't they absorb green light? We don't know. Firstly, it's important to know that this light-to-plant energy process isn't terribly efficient. Plants don't use very much of the energy they absorb at all, so they don't need to absorb more of the spectrum; they already have more than they need. So couldn't they use the green light as easily as the red and blue light? Why not use the green and red light, or the green and blue, or some other combination, or just one wavelength of light, but more efficiently? One hypothesis is that early on, other photosynthetic organisms commonly did absorb the green light, and that left a niche that early plants exploited, and then they thrived and just never needed to change since their particular light-absorbing strategy worked just fine.

So why visible light? Why not some other part of the spectrum besides what we can see? Well, infrared (so farther to the red side of the light spectrum) light could potentially cause heat damage to the cells, while ultraviolet (farther to the violet side of the light spectrum) light can damage cells by scrambling their biomolecular processes.

Plants use the visible light spectrum as a source of energy, and they absorb red and blue light for use in the plant while reflecting green light, which we see, which makes them green!

We don't know why they reflect and absorb those colors exactly, but it may have to do with competing with other light-absorbing organisms that did use green light; rather than compete for the light they simply went for another color, and never had to change because it worked well enough.Plants use very little of the energy they absorb anyway, so they don't really need to absorb all the visible light spectrum (but if they did, they would appear black!)

Most plants don't use much beyond the visible light spectrum because infrared and ultraviolet light could cause them harm.

Answer 2

Plants appear green because they contain chlorophyll, a pigment that absorbs light in the blue and red regions of the spectrum for photosynthesis. The green light is reflected, giving plants their green color. This adaptation is effective because the sun emits more energy in the blue and red wavelengths, making it the most efficient for photosynthesis.