From: altamira (altamira@ecpi.com)
Date: Sun Jul 16 2000 - 13:11:38 MDT
> -----Original Message-----
> From: owner-extropians@extropy.com
> [mailto:owner-extropians@extropy.com]On Behalf Of Michael S. Lorrey
>
> What method of calculating efficiency are they using? AFAIK, there is no
> natural occurence of chlorophyll based photosynthesis that exceeds 3%
> efficiency, and only a few specifically bred and engineered plants that
> go as high as 5% efficiency, which I had thought was the theoretical
> limit for chlorophyll based energy conversion.
I can't answer your question about method of measurement in this particular
case, but I'd be surprised if it were not through the measurement of
fluorescence emission. This is the method typically used to determine the
quantum yield of photosynthesis in plants, the quantum yield being the
number of electron-hole pairs generated per photon absorbed. "Electron-hole
pair" is a term used to describe the process that occurs when ionizing
radiation (light within a certain range of wavelengths in this case)excites
an electron out of its energy level. This is the first step in the process
of photosynthesis, in which carbon dioxide and water are converted into
carbohydrates (sugars).
Explanation of Fluorescence Emission: When light is absorbed by the leaf of
a plant, some of the light is absorbed by chlorophyll and used in
photosynthesis. The remainder is dissipated as heat and re-emission of
light. Fluorescence emission is the term used to refer to this re-emitted
light.
Here are some links if you want more detailed explanations:
simple experiment to measure quantum yield:
http://www.udel.edu/hodson/207/labmanual/FluorExp1.html
Field measurements of chlorophyll fluorescence:
http://www.nasatech.com/Briefs/May00/SSC00037.html
chlorophyll fluorescence defined:
http://www.h-saur.de/html/hauptteil_floures1.html
As far as I know, photosynthesis is not understood well enough for there to
be a theoretical limitation on efficiencies of artificial photosynthetic
processes.
Here's a pretty good simple explanation of photosynthesis which includes
both C3 & C4 pathways.
http://buglady.clc.uc.edu/biology/bio104/photosyn.htm
Bonnie
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