How does the membrane around a cell help regulate the internal makeup of the cell? With the Membrane Diffusion: Dialysis Demonstration—ChemTopic™ Lab Activity, compare the diffusion of small and large molecules across a semipermeable membrane to illustrate the process of diffusion in cells. Available as part of the Biochemistry: The Molecules of Life—ChemTopic™ Labs digital collection. Click the Price link for digital collection pricing.