A cell will swell up if (a) The concentration of water molecules in the cell is higher than the concentration of water molecules in the surrounding medium (b) The concentration of water molecules in the surrounding medium is higher than the water molecules concentration in the cell

Answer: The answer is option b – The concentration of water molecules in the surrounding medium is higher than the water molecules concentration in the cell.  A cell swells up when endosmosis takes place. Endosmosis means when water molecules move from the outside to the inside of the cell with help of the cell membrane. For Instance, the passage of water from roots hair cells to cortical cells of the roots.