Isotonic solutions describe what in terms of solute and water, resulting in no net movement of water?

• A. Equal solute and equal water; no net movement of water
• B. Higher solute outside; water moves into the cell
• C. Higher water outside; water moves out of the cell
• D. The membrane becomes impermeable to water

Answer: (A)

Osmosis and how water moves across a membrane define this idea. An isotonic solution has the same solute concentration as the inside of the cell, so the driving force for water to move is essentially equal on both sides. Water moves in at the same rate it moves out, giving no net change in cell volume. That balance keeps the cell’s size stable.

To connect this to other scenarios: in a hypertonic situation, the outside solution has more solute, so water leaves the cell and it shrinks. In a hypotonic situation, the outside has less solute, so water enters and the cell swells. The concept isn’t about the membrane becoming impermeable to water; instead, it’s about the solute balance driving water movement.

So, isotonic describes equal solute concentration across the membrane, leading to no net movement of water.