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BIOM 2101 Physiology, Fall 2009
Take home part of Test I
You may
NOT
work together on these problems.
You may use your notes or textbook and a
calculator but you may not get any assistance from another person or copy someone else’s work.
Show all your work in a neat, organized fashion.
1.
The total flux of O
2
across the total surface area of all of the capillary membranes at rest is 4
cm
3
O
2
/ sec. If the diffusivity of O
2
is 1.5 x 10
5
cm
2
fluid/sec and the concentration gradient is
0.6 cm
3
O
2
/(cm
3
fluid x cm fluid), what is the total area of the membrane predicted by Fick's
first law of diffusion?
(Be careful with your units; physiological gas concentrations are often
given in volume of gas dissolved rather than moles.)
J
=
D
A
dC/dx
Total flux =  diffusivity x area x concentration gradient.
Compare this area with something else
you are familiar with, e.g. the area of a floor of one room where you live; is the calculated area
comparable in size? much smaller? much larger?
Is this surprising to you?
2. Let’s derive a concentration profile, C(x),
for some substance across a thin lipid bilayer in a
steady state.
In addition to Fick’s law we used in class, another equation which governs
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 Fall '09
 ADAMS

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