A solution with a higher solute concentration than the cell interior causes water to move out of the cell; this solution is called

• A. Hypotonic solution
• B. Hypertonic solution
• C. Isotonic solution
• D. Osmotic solution

Answer: (B)

Tonicity and osmosis determine how water moves across a cell membrane. When the solution outside the cell has a higher solute concentration than the inside, water tends to move out of the cell to balance the solute levels. Because water is moving toward the higher solute concentration, the cell loses water and shrinks. This situation is described as hypertonic. If the outside solution had fewer solutes, water would move into the cell and it would swell (hypotonic). If solute concentrations were equal on both sides, there would be no net water movement (isotonic). The term osmotic solution isn’t standard; we describe this situation by saying the outside solution is hypertonic. Therefore, the described scenario corresponds to a hypertonic solution.