The correct option is B. Osmosis. Detailed Explanation: What is Osmosis? Osmosis is the movement of water molecules across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process occurs until there is an equal concentration of solute on both sides of the membrane. The selectively permeable membrane allows water to pass through while restricting the movement of solute particles. Why is Osmosis the Correct Answer? 1. Driving Force: Osmosis is driven by differences in solute concentration. When there is a higher concentration of solute on one side of the membrane, water moves toward that side to balance the concentration of solute. This movement continues until equilibrium is reached.

1. Selectively Permeable Membrane: The term "selectively permeable" refers to the ability of the membrane to allow certain substances (like water) to pass while blocking others (like larger solute molecules). This characteristic is crucial for osmosis, as it specifically involves the movement of water.
2. Biological Importance: Osmosis is vital for maintaining cell turgor pressure in plant cells, regulating hydration in animal cells, and facilitating various physiological processes in living organisms.

Why the Other Options are Incorrect: A. Active Transport - Definition: Active transport is the movement of molecules across a membrane against their concentration gradient, which requires energy (usually in the form of ATP). - Why It's Wrong: Active transport does not involve the movement of water and is not driven by differences in solute concentration. Instead, it moves solutes from areas of lower concentration to areas of higher concentration, which is the opposite of what occurs in osmosis. C. Facilitated Diffusion - Definition: Facilitated diffusion is the process by which substances move across a membrane with the help of transport proteins, from an area of higher concentration to an area of lower concentration, without the use of energy. - Why It's Wrong: While facilitated diffusion does involve the movement of substances down their concentration gradient, it does not specifically refer to the movement of water. Osmosis is a specific type of facilitated diffusion that pertains only to water molecules. D. Endocytosis - Definition: Endocytosis is a process by which cells engulf substances from their external environment, forming a vesicle to bring them into the cell. - Why It's Wrong: Endocytosis is not related to the movement of water across a membrane. It involves the uptake of larger particles or fluids and does not depend on solute concentration gradients. Summary of Key Points:

• Osmosis is the movement of water across a selectively permeable membrane driven by solute concentration differences.
• It is essential for maintaining cellular functions and homeostasis.
• Active transport and facilitated diffusion do not specifically involve water movement, while endocytosis pertains to the uptake of larger particles.
• Understanding osmosis is crucial for grasping how cells interact with their environment and maintain balance.

This thorough understanding of osmosis will help you in various biological contexts, especially in cell biology and physiology.