The correct option is C. Osmosis. Detailed Explanation: What is Osmosis? Osmosis is the process by which water molecules move across a selectively permeable membrane. This movement occurs 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). The goal of osmosis is to equalize the solute concentrations on both sides of the membrane. Why is Osmosis the Correct Answer? 1. Selectively Permeable Membrane: Osmosis specifically involves the movement of water through a membrane that allows water to pass but restricts the movement of solutes. This is a key characteristic of osmosis.

1. Concentration Gradient: The movement of water in osmosis is driven by the concentration gradient of solutes. Water moves to dilute the area with a higher concentration of solute, thereby attempting to balance the concentrations on both sides of the membrane.
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 - 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 its concentration gradient, not against it. B. Facilitated Diffusion - Definition: Facilitated diffusion is the process by which substances move across a membrane with the help of transport proteins, but it still occurs down the concentration gradient and does not require energy. - Why it's Wrong: While facilitated diffusion involves the movement of substances (like glucose or ions), it does not specifically refer to the movement of water. Osmosis is the specific term 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. This process requires energy. - Why it's Wrong: Endocytosis is not related to the movement of water across a membrane but rather involves the uptake of larger particles or fluids into the cell. Summary of Key Points:

• Osmosis is the movement of water from an area of lower solute concentration to an area of higher solute concentration across a selectively permeable membrane.
• It is a passive process that does not require energy.
• Other processes like active transport and endocytosis involve energy and do not describe the movement of water specifically.
• Facilitated diffusion involves transport proteins but does not pertain to water movement.

Revision Summary:

• Osmosis is the movement of water across a selectively permeable membrane.
• It occurs from low solute concentration to high solute concentration.
• Osmosis is a passive process, unlike active transport and endocytosis.
• Understanding the specific definitions of these processes is crucial for distinguishing them in exam questions.