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chlorophyll fluorescence

David Walker David at alegba.demon.co.uk
Tue Dec 31 12:43:51 EST 1996

White light  (sunlight, normal artificial room lighting) is a
mixture of all of the colours of the rainbow including blue, red and
green. In white light, chlorophyll looks green because it absorbs
the blue and the red wavelengths and reflects and transmits the
green. However, when illuminated, chlorophyll molecules also get
excited. In this process light energy gets converted into electrical
energy just as it does in the photocell of a camera or solar cells
in a satellite. Some of this electrical energy is then converted
back into light (fluorescence) just as it is when you switch on a
fluorescent light. Chlorophyll fluorescence is a deep red colour.
You can see some of  this very easily if you illuminate a solution
of chlorophyll and view it from the side. If you view it from the
front, so much green light comes through the solution that the
retina in your eye is saturated and you can only see green.
Similarly, on a paper tissue, you can not easily see it from the
side and the green predominates.
	The red excited state from which chlorophyll fluorescence emanates
is the starting point, the driving force, of the chemistry of
photosynthesis. So ultimately, via the food we eat, it is what
drives you.

If you wish to see a really striking picture of chlorophyll
fluorescence look at the cover of

WALKER DA 1987 The use of the oxygen electrode and fluorescence
probes in simple measurements of photosynthesis.  Oxygraphics
Limited, Sheffield, U.K. pp 1-145.

It ought to be possible to borrow this book from a library,
particularly if you also tell the librarian that the ISBN  number is
1 870 23200 but, if you  have a problem getting  hold of  a copy,
ask Richard at

richard at hansinst.demon.co.uk

bluej at juno.com wrote:
> Help??!  My biology class has a question; why does a lot of chlorophyll
> in a container look red?  The chlorophyll should look green, but our
> teacher put a lot of chlorophyll into a container and asked, why is it
> red?  To add to the confusion, when our teacher used a tissue to absorb
> the chlorophyll, the chlorophyll looked green on the tissue.  So we are
> asking, why is it red?
> Any help would be appreceated,
> Thanks.                         please respond to bluej at juno.com

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