Re: Bubbles homework

Paul K. asked for explanations of the common observation that
bubbles form on the leaves of aquatic plants in still water but
seldom in moving water.

We have also been told that aquatic plants have gas-filled
channels within them called aerenchyma, that extend from the leaves
to the roots, that is, from photosynthetic tissue to non-photosyn-
thetic tissue.

Is it possible that the motion of gases within the aerenchyma is
facilitated by the motion of water around the plant?  If the aerenchyma
is not a continous thread of gas, but is interrupted by water blockages,
then physical manipulation of the plant, might enable the gas to pass
through these water blockages more quickly.
In effect, the water current outside
the plant could be giving the plant a massage, enabling the oxygen
produced in the leaves to travel to the non-photosynthetic tissues where
its concentration is lower.  During this "massage", the oxygen concentration
in the leaves falls, so that bubbles are not produced.

This idea might be tested by looking for the effect of sound waves, which
would be expected to similarly facilitate the motion of gas through the
aerenchyma with much less effect on the concentrations of oxygen and
carbon dioxide in the boundary layer.


Curtis Hoganson
Dept. of Chemistry, Michigan State University
East Lansing, MI 48824   517-355-9715 ext 260