In the context of passive transport, what is the primary mechanism by which water enters and exits a cell across the plasma membrane?

• A. Active transport via ATP-powered pumps that move water molecules against their concentration gradient
• B. Osmosis, often facilitated by aquaporin channels, driven by differences in solute concentration (water potential) across the membrane
• C. Endocytosis and exocytosis of bulk water in membrane-bound vesicles under resting conditions
• D. Simple diffusion of water through ligand-gated ion channels that open only in response to signaling molecules

Answer: (B)