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
It may seem like a perfect plant would absorb all the light available and therefore be black but there is no point for a plant to absorb more light than it has the chemicals, primarily water and CO2, to make food with and for most plants if they **were** black strong sunlight would cook them. Chlorophyll a, the primary pigment which directly photosynthesises does absorb green light but it absorbs red and blue light far more readily so leaves look green because they reflect more green light or allow it to pass through. Plants in lower light conditions tend to use other pigments to capture green light then pass the energy to the chlorophyll to turn into plant food. So red algae can live at lower depths because it has accessory photosynthetic pigments which absorb blue-green light which penetrates the water better and purple understory plants can survive without much direct sunlight because their accessory pigments absorb the green light reflected or passed through by the green leaves above them. Seaweeds can be brown or black because they absorb more light but are water cooled which prevents the heat denaturing their tissues.
As with everything in evolution chlorophyll a came about by chance. You could argue that plants on Earth **should** be purple, primarily absorbing the yellow-green light most abundant in the sun’s light and sheding the dregs at either end of the spectrum. Scientists have even theorised that the first photosynthesisers could have been purple, and green plants evolved to take advantage of the scraps of light they left behind, then out competed them.
the graph [here ](https://www.simply.science/images/content/biology/cell_biology/photosynthesis/conceptmap/Photosynthetic_pigments.html) shows the absorption spectra for some common photosynthesisers and accessory pigments, compare to the [spectrum of the sun’s electromagnetic irradiation](https://www.sciencedirect.com/topics/physics-and-astronomy/solar-spectra)
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