The correct option is B. Osmosis. Detailed Explanation: What is Osmosis? Osmosis is the process by which water molecules move across a selectively permeable membrane from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration). This movement continues until there is an equal concentration of solute on both sides of the membrane, achieving equilibrium. Why is Osmosis the Correct Answer? 1. Selectively Permeable Membrane: The question specifies a "selectively permeable membrane," which allows certain molecules (like water) to pass through while restricting others (like solutes). Osmosis specifically refers to the movement of water across such membranes.

1. Concentration Gradient: The movement of water in osmosis is driven by a concentration gradient. Water moves from an area where it is more abundant (lower solute concentration) to an area where it is less abundant (higher solute concentration). This is a fundamental characteristic of osmosis.
2. Passive Process: Osmosis is a passive process, meaning it does not require energy (ATP) to occur. Water moves naturally down its concentration gradient.

Why the Other Options are Incorrect: A. Active Transport: - Active transport is the movement of molecules across a membrane against their concentration gradient, which requires energy (ATP). Since osmosis involves movement down a concentration gradient, this option does not apply. C. Diffusion: - Diffusion is the movement of molecules (not specifically water) from an area of higher concentration to an area of lower concentration. While osmosis is a type of diffusion (specifically for water), the question specifically asks about the movement of water, making "osmosis" the more precise term. D. Facilitated Diffusion: - Facilitated diffusion is a type of passive transport that involves the movement of molecules across a membrane via specific transport proteins. While water can move through channels called aquaporins (which is a form of facilitated diffusion), the term "osmosis" is more appropriate for describing the overall process of water movement across a selectively permeable membrane. Summary of Key Points:

• Osmosis is the movement of water across a selectively permeable membrane due to a concentration gradient.
• It occurs from an area of lower solute concentration to an area of higher solute concentration.
• Osmosis is a passive process and does not require energy.
• It is distinct from active transport, diffusion, and facilitated diffusion, which involve different mechanisms or types of molecules.

Revision Summary:

• Osmosis is the movement of water across a selectively permeable membrane.
• It occurs down a concentration gradient (from low to high solute concentration).
• Osmosis is a passive process, requiring no energy.
• Distinguish osmosis from active transport, diffusion, and facilitated diffusion for clarity in understanding biological processes.