Tuesday, August 28, 2012

Why green leafs instead of black ?

Green chlorophyll and sunlight
Green nature wallpapers

The somewhat surprising question in the title comes from the fact that Nature could utilize sunlight more efficiently if chlorophyll would be black. By rejecting the green wavelength plants get their green colours but loose part of the energy arriving from the Sun .

Word chlorophyll is derived from Greek words χλωρος, chloros ("green") and φύλλον, phyllon ("leaf").

Chlorophyll is crucially important for life on planet Earth as it is in the core of photosynthesis. It is a very complicated molecular structure built on Magnesium atom with its antennae for catching photons. Chlorophyll is used by green plants and also by some important bacteria and algae.

Klorofylli A ja B torjuvat vihreän valon taajuuden
Why green?
According to modern understanding all natural chlorophyll has its origins in the earliest life forms when algae were producing it. But why they reject green light?

Evolutionary Biology is unable to explain why since for the survival of the fittest it would seem more efficient to utilize the entire spectrum leaving chlorophyll black. Shil DasSarma from the University of Maryland suggest that we should not view evolution as a strictly optimized engineering project. As in the case of chlorophyll being green, evolution is not natural engineering that automatically chooses the best fit. Rather, evolving life has to deal with the realities of the environment and accidents of life and is organic rather than mechanical. According to Berman life forms evolve according to the conditions, limitations and possibilities given by reality and not by pure utilitarian logic and natural laws aimed at fitness peak.

Early life on Earth may have been a theatre for bitter fight for survival of the fittest in competition for energy with possibly dominating single cell arkhea that used especially green light through retinal (vitamin A aldehyde) molecule. Perhaps competition from such pink life forms pressured algae to evolve towards chlorophyll processes that reject green light. (Why would energy form a given color in the spectre of sun light be exclusive, though?)
(Read more about DasSarma's views in LiveScience 2007).

Scientific research progresses in this way by questioning also apparently self-evident facts and by suggesting new and challenging theories and hypotheses.  In the evolution of Evolutionary Biology some ideas survive, grow and develop while others wither and die and are thrown in the dust bin of the history of science.

Theological comment
And God said, “Let the water under the sky be gathered to one place, and let dry ground appear.” And it was so. God called the dry ground “land,” and the gathered waters he called “seas.” And God saw that it was good.

Then God said, “Let the land produce vegetation: seed-bearing plants and trees on the land that bear fruit with seed in it, according to their various kinds. ” And it was so. The land produced vegetation: plants bearing seed according to their kinds and trees bearing fruit with seed in it according to their kinds. And God saw that it was good. And there was evening, and there was morning —the third day.
Genesis 1:9-13 NIV
It would be rather sad if the leafs of the plants were black and grey, wouldn't it?

So let us praise the Lord for the green colour of chlorophyll that together with the majestic Sun create not only oxygen and sugar for all living creatures but also make the Nature so beautiful in the eyes of us people created in His image!

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