The correct option is C. Osmosis. Explanation of the Correct Answer Osmosis is the process that specifically describes the movement of water across a selectively permeable membrane. This movement occurs in response to differences in solute concentration on either side of the membrane. Here’s a step-by-step breakdown of why osmosis is the correct answer:

1. Definition of Osmosis: Osmosis is defined as the passive movement of water molecules from an area of lower solute concentration (where there are fewer solute particles) to an area of higher solute concentration (where there are more solute particles) through a selectively permeable membrane. This movement continues until equilibrium is reached, meaning the solute concentrations on both sides of the membrane become equal.
2. Selectively Permeable Membrane: A selectively permeable membrane allows certain molecules (like water) to pass through while restricting others (like solutes). This property is crucial for osmosis, as it enables the differential movement of water based on solute concentration.
3. Driving Force: The driving force behind osmosis is the concentration gradient of solutes. Water moves to dilute the higher concentration of solute, which is a natural tendency of solutions to reach equilibrium.
4. Passive Process: Osmosis is a passive process, meaning it does not require energy (ATP) to occur. Water moves along its concentration gradient, which is a fundamental characteristic of passive transport mechanisms.

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 (usually in the form of ATP). Since osmosis involves the movement of water down its concentration gradient (from high to low), it does not fit the definition of active transport. B. Facilitated Diffusion: - Facilitated diffusion is a type of passive transport that involves the movement of specific molecules across a membrane via protein channels. While it is also a passive process, it specifically refers to solutes (like glucose or ions) moving down their concentration gradient, not water. Therefore, it does not accurately describe the movement of water. D. Endocytosis: - Endocytosis is a process by which cells engulf substances from their external environment, forming a vesicle to bring them into the cell. This process is energy-dependent and does not involve the movement of water across a membrane in response to solute concentration. Thus, it is not relevant to the question. Summary of Key Points

• Osmosis is the movement of water across a selectively permeable membrane driven by differences in solute concentration.
• It is a passive process that does not require energy.
• Water moves from areas of lower solute concentration to areas of higher solute concentration.
• Other processes like active transport, facilitated diffusion, and endocytosis do not accurately describe the movement of water in this context.

This understanding of osmosis is crucial for various biological processes, including cellular hydration, nutrient absorption, and the maintenance of homeostasis in living organisms.