Osmosis. The movement of water molecules through a selectively permeable membrane from a region of high water concentration to low water concentration is called osmosis. I am hungry. Let us understand osmosis by taking some raisins. Raisins. Put some raisins in water. Raisins swell, indicating that they have absorbed water. Rewind. There was low water concentration inside the raisins. Before. After. As a result, they absorbed water and swelled. Such a solution where there is higher water concentration outside the cell is called a hypotonic solution. I do not like raisins. Let us place these raisins in sugar syrup. There is higher water concentration inside the raisins as compared to the sugar syrup. Water passes out from the raisins to the sugar syrup. Such a solution where there is lower water concentration outside the cell is called a hypertonic solution. The End.