Chlorophyll absorption

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

A nice article, in addition to the IR-reflection of chlorophyll:

xxxxxxxxxxxxxxxxxxxxxxxxxxxx
FROM: Marcangelo Puccio <mpuccio@xxxxxxxxxxxxxxxxxxx>
SUBJECT: Re: Night Vision Green?
DATE: Mon, 05 Apr 1999 21:40:11 -0700
NEWSGROUPS: sci.optics,sci.physics

Jim Mansfield wrote:

> In article <37091C73.7E228490@xxxxxxxxxxx>,
> Erik Max Francis  <max@xxxxxxxxxxx> wrote:
> >Thomas Jaworowski wrote:
>
> [snip night vison goggles being green - I haven't a clue why they are]
>
> >I haven't heard of that, but the Sun's frequencies peak at green, so it
> >makes sense that we would see best at around that peak frequency.  Also,
> >it's awfully convenient of chlorophyll (and other such molecules) absorb
> >energy around the peak frequency, in order to maximize the amount of
> >available energy available for photosynthesis.
>
> Doesn't there seem to be something conflicting about plant leaves _looking_
> green (ie, reflecting green light) and their absorbing energy at the
> Sun's peak frequency of green? Chlorophyll has absorption maxima in
> the blue and, to a lesser extent, in the red.
>
> -Jim
>
> --
> Jim Mansfield                          Internet: Jim.Mansfield@xxxxxx
> National Research Council of Canada    Phone:    (204) 984-5191
> Institute for Biodiagnostics           Fax:      (204) 984-5472
> http://www.ibd.nrc.ca/~mansfield/

Yes - you are right.

Plants photosynthesize poorly at best if illuminated by light at around 530
nm.  The following numbers are rough, but peak absorption in the red end is at
around 650 nm for Chlorophyll-a and at around 670-680 for Chlorophyll-b.
Peaks in the blue end are at around 440 and 460, respectively, with absorption
minima between 500 and 600 nm.  Some plants have 'accessory pigments' that are
able to absorb light pretty well in the 500 nm range (i.e., carotenoid piments
like beta carotene).  These form part of an 'antenna complex' that channels
energy from these other wavelengths to the chlrorophyll molecules that are the
core of the photosystems.  Some aquatic 'plants' (algae, actually) have
radically different absorptions that reflect the fact that certain wavelengths
of light are absorbed or reflected from sea water (i.e., red and golden algae
or 'seaweeds').

Not that this is a photobiology newsgroup... just had to comment!


-Marco


--                 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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