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Re: Homework Assignment
Everybody who tackled the problem correctly got the idea about the boundary
layer being much thinner when the water was in motion over the leaves
allowing the oxygen to diffuse out more rapidly. The stagnent layer around
the leaves acts as a thicker barrier once the concentration of O2 increases
in it. However, there are some other considerations:
(1) When the water is still, is the CO2 diffusing in faster than the O2 can
diffuse out? It would seem so, because of the production of bubbles. The
process of photosynthesis puts out one molecule of oxygen for every
molecule of carbon dioxide taken in. However, the solubility of CO2 is
greater than that of oxygen. If they both had the same rate of diffusion
through water, but O2 were less soluble, you could get the production of
bubbles for that reason, alone. However, I am pretty sure that CO2 also
diffuses faster, because it can diffuse in several forms (dissolved CO2,
carbonic acid, and bicarbonate ion). Chemists: back me up! I'm too old
and feeble to look up solubilities and diffusion rates. Thanks.
(2) when the water is moving over the leaves, shouldn't it allow the CO2 to
diffuse in even faster than it was before? And, if this happens, wouldn't
you have an increase in O2 production, and still have production of
bubbles? My hypothesis is that photosynthesis was already CO2-saturated in
the stagnent condtion, and so increasing availability of CO2 by decreasing
the boundary layer did not increase the rate of photosynthesis. Somewhere
in this is the making of some kind of test or evaluation to determine if
there is any benefit for a given species of aquatic plant to increasing the
CO2 content, but I don't have the time or energy right now to work it out.
Possibly this could be another homework assignment. :-)
You all get a B because I have a reputation as an academic meanie to
maintain! :-(
Paul Krombholz Tougaloo College, Tougaloo, MS 39174
Goofing off instead of working in pleasant, although cooler, Jackson,
Mississippi.