Dear Editor:
The article by Lankford and Friedrichsen (2012) that appeared in the August issue of The American Biology Teacher (74:392–399) does an excellent job summarizing a variety of hands-on activities that can be used to teach diffusion and osmosis. These “representations” will provide a valuable addition to a teacher’s repertoire. I was particularly impressed that the authors warned teachers that convection, rather than diffusion, was also responsible for molecular motion in some of their representations. However, I urge teachers to use caution when defining osmosis as water moving from an area of greater water concentration to an area of lesser water concentration. Although this is a simplistic way for students to understand the concept of osmosis, it is not always true. A simple example shows why.
Consider an osmometer constructed of a glass tube attached to a semipermeable membrane sac that is suspended in a beaker of water. Because...
University of California Press