The diffusion of water through a selectively permeable membrane is called ______.

Correct option is C

The correct answer is (C) Osmosis

Explanation:
• Osmosis is a specific type of passive biological transport. It is explicitly defined as the net movement (diffusion) of a solvent (usually water) across a selectively permeable membrane.
• Water molecules move from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution) until equilibrium is reached.
• This process is vital for cellular survival, as it dictates how cells absorb water and maintain turgor pressure (especially in plants).

Information Booster:
• Tonicity: The direction of osmosis depends on the tonicity of the surrounding fluid. In a hypotonic solution, water enters the cell (it swells). In a hypertonic solution, water leaves the cell (it shrinks). In an isotonic solution, there is no net movement.
• Reverse Osmosis (RO): By applying mechanical pressure greater than the osmotic pressure on a concentrated solution, water can be forced backward through a membrane. This is how RO water purifiers work.

Additional Knowledge:
• Option A (Transpiration): This is the biological process by which water is lost in the form of water vapor from the aerial parts of plants (stomata in leaves).
• Option B (Active transport): This requires energy (ATP) to move molecules against their concentration gradient, unlike osmosis which is entirely passive.
• Option D (Diffusion): Diffusion is the general movement of particles from high to low concentration. Osmosis is a specialized subset of diffusion restricted exclusively to solvents crossing a membrane.