On the left side, we have pure water. On the right side, we have water as well as our additional solute molecules. So these green molecules are solute molecules, for example, our sodium ions. Now, separating the left side from the right side is a semipermeable membrane. And the semipermeable membrane has small pores that allows the movement of water molecules but does not allow the movement of these solute molecules. So the green dots cannot actually move across the semipermeable membrane.