Can eating large amounts of sugarless candy and gum lead to diarrhea? How does Milk of Magnesia work? How does penicillin kill bacteria? These are some of the questions that students answer in this series of lessons on diffusion and osmosis. To begin the unit, students predict the results of a demonstration involving the relationship between soaking French fries in salt water and crispiness. To understand this relationship, students investigate the permeability of cell membranes by designing their own investigations using dialysis tubing. This investigation is a revised, inquiry version of the traditional lab found in many high school textbooks. To visualize the movement of molecules and the resulting effect on the cellular level, students use the innovative molecular modeling software, "Molecular Workbench." In the "Molecular Workbench" activities, students interact with dynamic computer models of diffusion, osmosis, and 3-D representations of molecules; observe the interactions and the net flow of molecules in air, in cells, and across a cell's semi-permeable membrane; and learn about the properties of the molecules. Students then apply their knowledge of osmosis to the novel situations listed above. The authors have found that students develop a deep conceptual understanding of diffusion and osmosis that they continue to draw upon throughout the year. (Contains 3 tables and 3 figures.)