Osmosis is defined as which of the following?

• A. The diffusion of water across a semipermeable membrane
• B. The active transport of solutes
• C. The diffusion of solutes across a membrane
• D. The diffusion of gases across membranes

Answer: (A)

Osmosis is the diffusion of water across a semipermeable membrane. Water moves from where there is more water (lower solute concentration) to where there is less water (higher solute concentration) to help equalize solute concentrations on both sides. This process is passive, needing no energy input, and it depends on a membrane that lets water pass but restricts many solutes. The other options describe diffusion of solutes, gas diffusion, or active transport, none of which capture the movement of water specifically across a membrane due to solute differences.