When grapes are soaked in water, the grapes then swell up because grape's cells have a high concentration of solutes in comparison to the water. In other words, grapes have low concentration of solvent (that is water molecules ) in comparison to the concentration of solvent in water. In this situation, there will happen a process known as osmosis in which water molecules moves from a region of concentration of water to a region of low concentration of water through a semipermeable membrane. (the cell membrane of the grape's cell is also semipermeable,which only allows solvent molecules to pass through it)