On Wed, Mar 10, 2010 at 12:18 PM, Russell McMahon <apptechnz@gmail.com> wro=
te:
> So far so good. BUT.
> 1. =A0How does a given gas "know" the pp of it's fellow on the other side=
 of
> the membrane to the exclusion of all other gases at other pp's which may =
be
> present? ie what makes Oxygen "see" Oxygen and not Nitrogen or CO2. What
> makes CO2 not "see" Nitrogen etc.

Keep in mind that your example is more complex due to other chemical
actors.  Hemoglobin strongly attracts oxygen and weakly attracts CO2.
So even if the other variables are the same, the side with the
hemoglobin is going to 'appear' to have a lower pressure/volume for
both gasses.

> 2. Is it possible to "spoof" a gas into reacting to another gas so that it
> alters its diffusion rate based on both the pp of the same gas on the oth=
er
> side AND also wholly or partially due to the presence of this other gas? =
If
> so how, and what are the criteria?

No, they both flow both ways across the membrane according to the
statistical likelihood of hitting a permeable spot during its random
motion.  They don't know about each other at all.

What you really need is a biological diode - a permeable membrane that
is more permeable one way than the other for a given target gas.

-Adam

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