Photosynthesis (The Path of Carbon in Photosynthesis and thePrimary Quantum Conversion Act of Photosynthesis) Page: 4 of 32
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tried to use this term a number of times without success, the reason being that
people take it for a typographical error and always change it; so I don't try any
more. ) In any case, I will give you briefly the results of these studies on the
path of carbon - the synthetical part - and then show you that particular point
in which these studies, which for a long time we thought were completely
divorced from the "photo" part of the reaction, have lead us to make a sugges-
tion, at least, of what the primary quantum conversion act of photosynthesis
is. This is what I am going to try to bring you today.
Let us briefly review the path of carbon in photosynthesis - how we have
studied it and what kind of information has arisen from this study. The method
of study in such a system as this is pretty straightforward. One simply
arranges a green plant of some sort in a steady state of photosynthesis. This
might be represented diagrammatically in Figure 2. The "plant" is placed in
a situation corresponding to the box and a steady state of photosynthesis is
set up; the plant absorbs CO2, light and water, and the CO2 is being converted
through a series of intermediates into reduced compounds (carbohydrates) of
some sort or other, evolving oxygen in a steady state condition. At a time
t = 0, we will inject the labeled carbon into the entering stream of CO2 and
trace its path along inside the leaf, or the green plant. It is quite clear that
if we wait long enough labeled carbon will find its way into carbohydrates and
other reduced materials of the plant. The experiment is to shorter the time
during which the carbon has been traveling along this road until we find the
earliest compounds into which that carbon is incorporated. Thus we are able
to trace the path along which it travels and the branches and cycles it might
In order to do this steady state experiment, it is necessary to have more
or less reproducible organisms, and Figure 3 shows our algae "farm". We
use green algae for this continuous culture system (although blue-green algae
and purple bacteria are sometimes used); these are harvested every day and
a new culture medium drawn in. Figure 4 will show the exposure apparatus.
The algae suspension is placed in this flat circular vessel which we call the
"lollipop" (for obvious reasons) and the light source is on either side passing
through the infrared filters; the CO2 is entering in continuous flow through a
bubbler tube. At a time t = 0 we allow radiocarbon to enter with the CO2, and
at suitable intervals of time we open the stopcock, draw out the algae suspen-
sion into alcohol and thus stop the biological reactions that are going on in as
Here’s what’s next.
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Calvin, Melvin. Photosynthesis (The Path of Carbon in Photosynthesis and thePrimary Quantum Conversion Act of Photosynthesis), report, November 22, 1952; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc879080/m1/4/: accessed June 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.