(N/A) When a cell has a higher water concentration than the surrounding medium,water moves out of the cell into the medium. This process is known as exosmosis,which causes the cell to shrink or become plasmolysed.
$(b)$ When a cell has a lower water concentration than the surrounding medium,water moves from the medium into the cell. This process is known as endosmosis,which causes the cell to swell or become turgid.
$(c)$ When a cell has an equal water concentration to its surrounding medium,there is no net movement of water across the cell membrane. The cell remains in an isotonic state,and its size and shape remain unchanged.