Osmosis is when water molecules move from a high concentration to a low concentration. Diffusion is when molecules move from a high concentration to a low concentration. In this experiment the plastic bag acted as the cell membrane and we were labeled as different substances. Some of us moved through the cell membrane wall, but some of us could not because of the molecules. However, the molecules are always in motion. I was glucose and I was able to move through the membrane, this is known as diffusion. The iodine evened out, there were iodine substances on both sides. The starch could not go through the membrane because of the substances that it contained.