Osmosis is defined as which process?

• A. Movement of solutes across a membrane through protein channels
• B. Endocytosis of water droplets
• C. Diffusion of water through a selectively permeable membrane
• D. Active transport of water using pumps

Answer: (C)

Osmosis is water moving across a membrane that only allows certain substances to pass, from where water is more plentiful (higher water potential, lower solute concentration) to where it is less plentiful (lower water potential, higher solute concentration). This is a passive process, meaning it doesn’t require energy. The key idea is that water, not solutes, diffuses through a selectively permeable membrane to balance concentrations on both sides. That’s why the correct description is diffusion of water through a selectively permeable membrane. Endocytosis, active transport of water, or movement of solutes through channels don’t describe osmosis.