A solution with a lower solute concentration than the cell interior is called

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

Answer: (A)

Think about tonicity and how water moves by osmosis. Water tends to move from where solute concentration is lower to where it is higher. If the outside solution has fewer solutes than the inside of the cell, the outside is hypotonic relative to the cell interior. Water then enters the cell to balance the concentrations, causing the cell to swell. So the best term for a solution with a lower solute concentration than the cell interior is hypotonic. If the outside had more solutes, it would be hypertonic and water would leave the cell; if the concentrations were equal, the net movement of water would be minimal (isotonic). The label osmotic solution is not a specific classification like hypotonic, hypertonic, or isotonic.