Daniel Carrera

Have you ever wonder why plants are green?

And no, the answer I’m looking for is not “stuff is green because it reflects green light and absorbs red and blue”. What I mean is, why in the world would plants choose to reflect green, when most of the sun light is in the green spectrum? Wouldn’t it make more sense or plants to absorb green?

Well, today I found a web page explaining this. I thought it was very interesting and wanted to share the link. In summary:

Why are plants green?

Because they appeared late, after a different organism had already developed green photosynthesis. The first plants (algae) lived in the water, below the non-green plants, so all they had available was red and blue.

Then why did green plants come to dominate the planet?

Because this new kind of plant also had the ability to use CO₂ from the atmosphere to make sugars. So although they were disadvantaged when it came to the light spectrum, they were superior over-all.

It is also interesting that plants have evolved to minimize the disadvantage of being stuck with the non-green spectrum. Plant leaves have a complex structure that makes light bounce around inside the leaves, so that each photon has multiple chances of being absorbed. For this reason, although chlorophyll only absorbs about 2% of incident green light, a leaf as a whole can absorb as much as 50%. For more on that point, see this page.