In this virtual lab, students explore diffusion by observing how molecules move across a selectively permeable dialysis tube. The student begins by preparing a dialysis tube filled with water and starch, sealing it, and placing it into a beaker containing water mixed with iodine potassium (IKI). Since IKI reacts with starch by turning black, the student uses this color change to determine whether diffusion has occurred. After a simulated soaking period, they analyze whether the solution inside the tube or in the beaker has darkened, providing insight into which molecules were able to cross the membrane. This experiment demonstrates passive transport and selective permeability in a controlled environment.