photosynthetic CO2 sources

[Douglas Jensen]

    As I get into the physiological portion of my General Botany course,
I am coming to a quandry that has bugged me for a few years.  I guess
it's time to show my physiological phailures publicly and to request
expert advice.
    The problem is this.  Water transport is generally powered by
transpiration.  This means that there is a constant flow of vapor out
the stomata when they are open.  However, we also teach that the carbon
dioxide for photosynthesis comes in through the stomata at the same
time.  I have a difficult time envisioning significant diffusion of CO2
going against a flow of water vapor.  Is there good support for an
atmospheric source of CO2?   Could enough carbon be transported through
the xylem as carbonate?  On the other hand, am I worrying about two
processes that do not interact significantly?

thanks,
Doug
--
Douglas P. Jensen
Assistant Professor of Biology
Converse College
580 East Main Street
Spartanburg, South Carolina 29302
(864)596-9123
fax: (864)596-9201


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