why dried raisins placed in water swell up
Dried raisins when kept in pure water swell up after some time due to endosmosis . The concentration of solutes in raisins is more than the outside so water move inside the raisin resulting in its swelling. Raisinsshrink in concentrated saline water due to exosmosis . As the concentration of solute is more outside i.e. in saline water as compared to raisin, so it looses water and shrinks to attain equilibrium.
Endo-osmosisement or movement of water from outside the raisins to the inside of the raisins cause them to swell up (there is a semi-permeable plasma membrane outside each cell which leads to this.....)