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Why Plants Are Green

802 views 4 replies 3 participants last post by  jeffkrol 
#1 · (Edited)
#2 ·
Second URL fails...

First one should be obvious to anyone who passed and remembers high-school physics.

Well, except for the part where they claim sunlight is primarily red and blue light mixed together. That's just a total lack of understanding of sunlight. There's more photons being emitted by the sun at green wavelengths than red.
 
#3 ·
Ancillary pigments tht do absorb green light pass their energy down to chlorophyll reaction centers. So green light is used, and sometimes in say shade environments or high light environments, used quite a bit.

Point is it is a bit more complicated than that:
Namely, red light is more effective than green light in white light at low PPFDs, but as PPFD increases, light energy absorbed by the uppermost chloroplasts tends to be dissipated as heat, while penetrating green light increases photosynthesis by exciting chloroplasts located deep in the mesophyll. Thus, for leaves, it could be adaptive to use chlorophylls as photosynthetic pigments, because, by having chlorophyll with a ‘green window’ the leaves are able to maintain high quantum yields for the whole leaf in both weak and strong light conditions.
http://pcp.oxfordjournals.org/content/50/4/684.full



What it means to these thin leaved aquatics is???

However, many spectra of absorptance (the absolute value of light absorption) measured with integrating spheres have shown clearly that ordinary, green leaves of land plants absorb a substantial fraction of green light (McCree 1972, Inada 1976, Gates 1980). It is also known that green light, once absorbed by the leaves, drives photosynthesis with high efficiency (Björkmann 1968, Balegh and Biddulph 1970, McCree 1972, Inada 1976). On an absorbed quantum basis, the efficiency or photosynthetic quantum yield of green light is comparable with that of red light, and greater than that of blue light. The difference between the quantum yields of green and blue light is particularly large in woody plants grown outdoors in high light. The question of how much green light is absorbed and used in photosynthesis by the green leaves of land plants has therefore been solved
Consequently, green leaves absorb much green light. Typical values of absorptance at 550 nm range from 50% in Lactuca sativa (lettuce) to 90% in evergreen broad-leaved trees (Inada 1976). The corresponding absorptance values for blue and red lights range from 80 to 95%.
 
#4 ·
Agreed, although those secondary pigments absorb less...

Plant leaves are green because they reflect more green light than any other color.. but you are right that they don't reflect all of it.

I still find it very strange that a page with a fundamental failure to understand the spectrum of sunlight is being hosted by MSU. I'd expect a more solid grasp of the subject from a high school student.


That said, the other site, UCSB, actually has a interesting theory as to why plants reflect a lot of green even though it is where the most energy is:

http://scienceline.ucsb.edu/getkey.php?key=500

Which makes some sense... if plants were black and absorbed all the light hitting them, they'd probably cook in full sun.
 
#5 · (Edited)
My only question is which pigment really is the main absorber of green.. Chlorophyll or carotinoids. Absorption spectrums in solvents isn't always the most diagnostic of things. ;)


but it does keep up my obsession w/ Cyan LED's ;)
 
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