When cells are in an isotonic solution, it means that the concentration of solutes outside the cells is the same as the concentration of solutes inside the cells. In this state, there is no net flow of water into or out of the cells. The water molecules move freely across the cell membrane, but the movement in and out of the cell is balanced. As a result, the cells maintain their shape and volume, and there is no change in the overall water content of the cells. This state is called "equilibrium" or "osmotic balance."
