Membrane Dynamics - Practice Exam Question

[Sara Meghji]

Hi everyone! I hope the semester is off to a nice start. Here is an old exam question about membrane dynamics to get you thinking about the material. As soon as enough people have posted responses, I'll post the answer.

Imagine a cell in which the membrane is impermeable to Na+ and Cl-, freely permeable to H2O, and moderately permeable to urea. The cell is happily floating in an isoosmotic solution of NaCl. Which one of the following would happen if you abruptly added urea to the solution bathing the cell?

a. The cell would swell and remain swollen.

b. The cell would shrink and remain shrunken.

c. The cell would swell, but after a brief period of time, it would return to its original volume.

d. The cell would shrink, but after a brief period of time, it would return to its original volume.

e. Adding urea would have no effect on the cell’s volume, not even briefly.