What is osmosis?

• A. The movement of particles from higher concentration to lower concentration, without energy input.
• B. The diffusion of water across a selectively permeable membrane from an area of higher water potential to lower.
• C. The diffusion of solutes from high to low concentration.
• D. The splitting of water molecules to release energy.

Answer: (A)

Osmosis is the movement of water across a selectively permeable membrane from an area of higher water potential to an area of lower water potential. It’s a passive process, so no energy is required. Water moves toward the side with more dissolved solutes (lower water potential) to help balance concentrations across the membrane. This is different from diffusion of solutes, which involves solute particles moving from high to low concentration, and from any process that splits water molecules to release energy, which is not osmosis.