What does tonicity refer to?

• A. The total concentration of solute particles in a solution
• B. The effect of a solution on cell volume
• C. The pressure needed to stop osmosis
• D. The concentration of impermeant solutes

Answer: (B)

Tonicity specifically refers to the effect that a solution has on the volume of cells when they are immersed in that solution. This concept is crucial in understanding how cells interact with their surrounding environments in terms of fluid movement. When cells are placed in solutions of different tonicity, the concentration of solutes relative to the cell's internal environment determines the movement of water across the cell membrane via osmosis.

For instance, in a hypertonic solution, the solute concentration outside the cell is higher than inside, leading to water moving out of the cell, causing it to shrink. Conversely, in a hypotonic solution, where the solute concentration is lower outside the cell, water moves into the cell, leading to swelling. An isotonic solution has equal solute concentrations inside and outside the cell, resulting in no net movement of water.

Understanding tonicity is vital for applications in biology and medicine, particularly in administering IV fluids and understanding cellular responses to different environments.