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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Shadow on August 03, 2014, 10:18:19 AM

Title: Absorption maximum of chlorophyll
Post by: Shadow on August 03, 2014, 10:18:19 AM
I read in a book the following: The wavelength at which the maximum radiation flux occurs, is for the Sun 501 nm. This is interesting, as with an absorption maximum in the blue-green part of the spectrum that is close to but not coincident with an absorption maximum in the spectrum for chlorophyll.

The 501 nm correspond approximately to the green light. If chlorophyll absorbs this wavelength, why is it green then? Doesn't it reflect green?
Title: Re: Absorption maximum of chlorophyll
Post by: Arkcon on August 03, 2014, 11:36:05 AM
The reference you've quoted seems to me to be the emission maximum of the sun.  The absorption maximum of chlorophyll happens to be elsewhere:  http://en.wikipedia.org/wiki/Chlorophyll#Spectrophotometry  I don't see why you think the two have to be absolutely connected.
Title: Re: Absorption maximum of chlorophyll
Post by: Shadow on August 04, 2014, 03:34:17 AM
I don't see any connection at all. The sentence must be wrong!
Title: Re: Absorption maximum of chlorophyll
Post by: Arkcon on August 04, 2014, 01:21:09 PM
Re-read it.  The statements, if not connected at all, don't have to be wrong. ;)
Title: Re: Absorption maximum of chlorophyll
Post by: Shadow on August 06, 2014, 09:05:00 AM
I think that chlorophyl mostly reflects light from the green light region.
Title: Re: Absorption maximum of chlorophyll
Post by: Arkcon on August 06, 2014, 01:53:42 PM
Yes.  And ...?
Title: Re: Absorption maximum of chlorophyll
Post by: Shadow on August 07, 2014, 09:58:21 AM
What? Sun mostly radiates green light and chlorophyll mostly reflects green light. Why?
Title: Re: Absorption maximum of chlorophyll
Post by: Arkcon on August 07, 2014, 01:28:33 PM
Quote from: Shadow on August 07, 2014, 09:58:21 AM
What? Sun mostly radiates green light and chlorophyll mostly reflects green light. Why?

Why not?

Did the entity in charge (either God or evolution, take your pick, I'm not here for an argument) make a mistake?
Title: Re: Absorption maximum of chlorophyll
Post by: Shadow on August 07, 2014, 01:51:30 PM
Wouldn't photosynthesis have the biggest efficiency if chlorophyll absorbs green light?
Title: Re: Absorption maximum of chlorophyll
Post by: rwiew on August 07, 2014, 02:26:09 PM
It would, if it was possible for evolution to come up with a system that would use it all / most of it without any associated dangers. Apparently it was not - the problem is if you absorb light energy into a system that is meant to convert it into chemical energy, you have a problem if you can't use all of it - side reactions might result, leading for example to damage to the photosystem, cellular components, DNA. It appears the green light was simply too intense for plants and it was better to make use of the less intense but safer red and blue components.
Title: Re: Absorption maximum of chlorophyll
Post by: Shadow on August 07, 2014, 03:12:31 PM
"but safer red and green components."
I think you have a typo here. Thanks for explaining.
Title: Re: Absorption maximum of chlorophyll
Post by: rwiew on August 07, 2014, 03:47:52 PM
Haha yes, good call!