The tendency of molecules to move from areas of more molecular concentration to areas of less, is called diffusion. The program contains demonstrations of liquid, gas, and solid diffusion. Computer animation explains what is happening at the molecular level. Osmosis experiments involve animal cells and their semi-permeable membranes. Plants depend on their environment for the proper amount of water diffusing into their cells in order to maintain a viable internal pressure. As long as the concentration of solutes remains greater either inside or outside a plant or animal cell, water diffuses either into or out of cells through its membrane to equalize the internal and external concentrations. The program provides clear explanations and excellent illustrations of this key biological process.