I mean, I know plants are green because chlorophyll is green. But why is that? Is that particular hue any better or more efficient for plants, light absobtion or energy transfer? Was it just random that these molecules happen to be green? Or is green really better than other colors for this job?
In: Biology
Because they absorb light that is red and blue leaving, leaving just green light to reflect back.
If you graph the frequencies of light that gets absorbed by plant in photosynthesis you will notice a few things:
First they absorb light mostly in the same part of the spectrum that we human use to see. That part makes sense because that is the part of the spectrum where the light emitted from the sun is the strongest so everything that makes use of it gets pushed by evolution to use that part of the spectrum.
A weird thing however is that plants don’t just absorb all the visible light. They absorb in two separate humps.
There are different types of chlorophyll which absorb slightly different wavelengths but hey all follow the same broad pattern:
Broadly one hump is in the 400nm to 500nm range and another hump in the 600nm to 700nm range leaving the part in the middle alone.
400-500 nanometer is blue from violet to blue with a slight green tine and 600-700 nanometer is orange to red.
Chlorophyll a has a tiny hump in the yellow part of the spectrum and Chlorophyll b absorbs a small amount of light throughout the entire visible spectrum and extends into the ultra violet part beyond.
Chlorophyll doesn’t use green light and thus reflects it back and appears green.
This is a bit weird because that means plants basically leave money on the table as far a solar energy is concerned.
It doesn’t seem to be entirely clear why that is.
One theory I have heard is that the ancestor to today’s chlorophyll evolved back when it was its own organism in an environment where green light was already absorbed by something else that no longer is around and evolution never filled the gap.
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