why is green photosynthesis so dominant?

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mattw
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why is green photosynthesis so dominant?

Post by mattw » Tue May 15, 2007 8:09 pm

Red algae use phycoerythrin. Some other plants like red maples use what pigments?
Why are plants that use red and yellow light mostly so dominant (cholrophyll a and b and carotenoids)? Why haven't a number of photosynthetic pigments developed over Earth's history? So why aren't there many leaf colors --or are there? Purple Earth was so long ago. Why haven't many photosynthetic pigments been chanced upon, since then. :D

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Post by mattw » Tue May 15, 2007 8:23 pm

woops --red and blue light!

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mith
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Post by mith » Tue May 15, 2007 9:26 pm

Living one day at a time;
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
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James
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Post by James » Tue May 15, 2007 10:29 pm

Evolution doesn't try new things to be quaint. Once a successful mechanism is established it will probably hang around.

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Post by Darby » Wed May 16, 2007 5:25 pm

There's a very good chance that of all the photosynthetic pigments that have evolved, the chlorophylls best use the range of frequencies available at and above the surface of the oceans. The other pigments work better at depth, where only some frequencies penetrate, or they get used as supplements to chlorophyll.

Might there be some black pigment that absorbs all frequencies? Maybe, but it doesn't appear to have evolved on Earth.

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Post by kotoreru » Wed May 16, 2007 5:39 pm

The problem with a black pigment would be that the high extinction co-efficient it present to irradiance would be such that the delicate pigments would be, simply, damaged (basically - it soaks up all the light).

Light on land is relatively predictable compared to the oceans. A cell in the oceans may go from 1600+ PFD (photon flux density) to <10PFD in a matter of minutes.
The delicate little pigments necessary to make use of low level, attenuated, light at depth simply cannot 'put up with' high irradiance at the surface.

My former teacher once referred to this as the 'Goldilocks analogy': not too bright, not too dark, but just right...

(sorry - I've just had an exam on precisely this...)
"What are humans if they don't learn at University? Animals, yes."

^^One of my ex-girlfriends said that. I stress the ex part.

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Post by Darby » Thu May 17, 2007 7:47 pm

It seems like if that hypothesis was true, then nothing would have black pigments - or pigments that absorb particularly energetic frequencies, such as the purples or ultraviolet. As it is, chlorophyll absorbs a pretty wide range of frequencies, at a heavy peak of intensity.

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Post by JDavidE » Thu May 17, 2007 11:11 pm

Darby wrote: As it is, chlorophyll absorbs a pretty wide range of frequencies, at a heavy peak of intensity.


Precisely. Although there are likely to be specialists, it is far more practical to use morphology or structure to moderate the available light.

Low-light conditions producing large leaves (usually widely spaced).

Intense light producing masses of leaves (to create a dapple effect) of small size.

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Post by kotoreru » Fri May 18, 2007 12:58 pm

Not all photosynthetic matter is on land, people...
"What are humans if they don't learn at University? Animals, yes."

^^One of my ex-girlfriends said that. I stress the ex part.

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Post by Darby » Fri May 18, 2007 3:39 pm

Aquatic environments have been mentioned repeatedly in the thread, but the original question was about the predominant pigments, which are found near the ocean's surface and in land plants.

What exactly does "delicate" mean, applied to a molecule?

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kotoreru
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Post by kotoreru » Sat May 19, 2007 11:55 am

You have a molecule that is 'designed' to mop up relatively high energy photons - chlorophyll et al are not simply molecules, and cells are chock full of repair mechanisms to sustain them.

I think that constitutes delicate...

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Post by Ultrashogun » Sun Jul 15, 2007 2:59 am

I think the great abbundance of light near the waters surface and on dry land removes the need to absorb the highest energy light.

Red and Brown Algea live in greater depths so their pigments are specialized to absorb the light that reaches those depths.

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