Osmosis is the process in which a cell either gains or loses a large amount of water due to its environment. In experiment one where the first set gained mass, the cells were in a hypotonic environment meaning that there was more solute (e.g. salt or other solid material) in the cell than outside of it, so the water was rushing into the cell towards the solids faster than the cell could push it out. The second set was the exact oppisite, where it was in a hypertonic environment, making water leave the cell faster than it was able to replenish it. The third set however, is in an isotonic state. The cell has achieved dynamic equilibrium where the same amount of water molecules that are flowing in are also flowing out so the cell doesnt change size. The student who thought the third experiment hadnt worked was incorrect.