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 to an area of higher solute 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: Osmosis specifically involves a membrane that allows water to pass through while restricting the movement of solutes (like salts or sugars). This characteristic is crucial because it differentiates osmosis from other transport processes.

1. Concentration Gradient: The driving force behind osmosis is the concentration gradient of solutes. Water moves to dilute the area with a higher concentration of solute, which is a fundamental principle of osmosis. This is a passive process, meaning it does not require energy.
2. Biological Importance: Osmosis is vital for many biological processes, including maintaining cell turgor in plants, regulating blood pressure in animals, and facilitating nutrient absorption in cells.

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: Osmosis does not require energy and moves water along the concentration gradient, not against it. Therefore, it does not fit the definition of active transport. 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. - Why It's Wrong: While facilitated diffusion does involve the movement of substances down their concentration gradient, it does not specifically refer to water. Osmosis is the specific term used for water movement. D. Endocytosis - Definition: Endocytosis is a process by which cells engulf substances from their external environment, bringing them into the cell in vesicles. - Why It's Wrong: Endocytosis is not related to the movement of water across a membrane due to concentration differences. It involves the uptake of larger molecules or particles, not the passive movement of water. Summary of Key Points:

• Osmosis is the movement of water across a selectively permeable membrane due to concentration differences.
• 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 crucial for maintaining cellular functions and homeostasis in living organisms.

By understanding these concepts, you can better grasp the importance of osmosis in biological systems and differentiate it from other transport mechanisms.