Re: Chlorophyll absorption

[George L Smyth <GLSmyth@xxxxxxx>]

Willem-Jan Markerink wrote:
> 
> 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

But chlorophyll is not the reason for the strong reflectance of infrared
radiation.  The strong reflection is due to the air pockets between the cells
within the leaf.

george

-- 

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