How is osmosis defined?

• A. Movement of solutes across a membrane
• B. Active transport of water in cells
• C. Passive movement of water across a selectively permeable membrane
• D. Diffusion of gases in the bloodstream

Answer: (C)

Osmosis is accurately defined as the passive movement of water across a selectively permeable membrane. This process occurs when there is a concentration gradient of solute on either side of the membrane—water moves from an area of lower solute concentration to an area of higher solute concentration in an attempt to equalize solute concentrations on both sides. Importantly, this movement does not require energy input, distinguishing it as a passive process. The selectively permeable membrane allows the free passage of water molecules while restricting the movement of solute molecules, which facilitates the osmotic process. This definition highlights the crucial role of water in biological systems and its importance in maintaining cellular homeostasis.