Which process moves water molecules across the cell membrane down their concentration gradient?

• A. Endocytosis
• B. Osmosis
• C. Active transport
• D. Facilitated diffusion

Answer: (B)

Verified step by step guidance

1. Identify the key concept: The movement of water molecules across the cell membrane down their concentration gradient is a specific type of passive transport.
2. Understand the term 'concentration gradient': This refers to the difference in the concentration of a substance between two areas. Water moves from an area of high concentration to an area of low concentration.
3. Define osmosis: Osmosis is the process by which water molecules move across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration, without the use of energy.
4. Differentiate osmosis from other processes: Endocytosis and active transport require energy to move substances against their concentration gradient, while facilitated diffusion involves the use of transport proteins but does not specifically refer to water movement.
5. Conclude with the correct process: Osmosis is the correct process for moving water molecules across the cell membrane down their concentration gradient.