Define osmosis.

Define osmosis.

• A. Movement of water across a selectively permeable membrane from an area of higher water potential to an area of lower water potential.
• B. Movement of solutes across a selectively permeable membrane using ATP.
• C. Diffusion of water from an area of low concentration to high concentration.
• D. Active transport of water using membrane pumps.

Answer: (A)

Osmosis is the diffusion of water across a selectively permeable membrane from an area of higher water potential to an area of lower water potential. Water moves this way because it flows toward where its potential energy is lower, which typically means a region with more solute and less free water. The membrane lets water pass but blocks many solutes, so the net movement balances solute concentrations on both sides without using energy. The other descriptions describe movement of solutes with energy (active transport), or water moving in the opposite direction, or water movement that requires pumps—none of which are osmosis.

Osmosis is the diffusion of water across a selectively permeable membrane from an area of higher water potential to an area of lower water potential. Water moves this way because it flows toward where its potential energy is lower, which typically means a region with more solute and less free water. The membrane lets water pass but blocks many solutes, so the net movement balances solute concentrations on both sides without using energy. The other descriptions describe movement of solutes with energy (active transport), or water moving in the opposite direction, or water movement that requires pumps—none of which are osmosis.