The correct option is (b) The concentration of water molecules in the surrounding medium is higher than water molecules concentration in the cell.
The cell swells up when endosmosis occurs. Endosmosis is when the water molecules move from the outside to the inside of the cell through the cell membrane. Example – Passage of water from root hair cells to cortical cells of the root. Water molecules move along the concentration gradient, that is, from higher concentration to lower concentration. So, for a cell to swell, it has to be placed in a hypotonic solution.
- When the solvent’s movement takes place from outside to inside, the all (inward movement) process is endosmosis. It occurs in a hypotonic solution and causes the swelling of the cell.
- When the solvent’s movement takes place from inside to outside the cell (outward movement), the process is exosmosis. It occurs in a hypertonic solution. It results in the shrinkage of the cell.