Osmosis is the diffusion of water. A solution with high solute concentration is hypertonic or hyperosmotic. A solution with lower solute concentration is hypotonic or hypoosmotic. Hypotonic solutions cause cells to swell, hypertonic solutions cause cells to shrink. When internal cellular solute concentration is equal to the external solute concentration, the internal and external fluids are isotonic or isosmotic.
Plant cells are generally hypertonic compared to their fluid environment.
Therefore, water tends to enter the cell causing internal pressure called turgor . In a hypertonic solution, plant cells lose volume and shrink causing their plasma membrane to pull away from the cell wall causing plasmolysis . In this case, the solutes bind to specific membrane protein carriers. These carriers undergo specific conformational changes. Molecules that require facilitated diffusion are sugars, amino acids, phosphorylated compounds, etc.