Explain why :
Resins swell up when kept in water.
Resin swells up when kept in water, due to endosmosis.
Endosmosis: When a cell is placed in hypotonic solution (solute is less in amount and solvent is more in amount), water molecules move from outside to inside the cell through semipermeable membrane, this process is known as endosmosis.
Due to endosmosis, cells get swollen.