If plant cells placed in water neither take nor lose water, it means they are in a state of isotonic equilibrium. This implies that the strength of the sap (internal solution) is equal to the strength of the external solution (water).

Here's why:

* Osmosis: Water moves across a semi-permeable membrane (like the cell membrane) from an area of high water concentration to an area of low water concentration. This movement is driven by the difference in solute concentration, trying to achieve equilibrium.

* Isotonic solution: An isotonic solution has the same solute concentration as the cell's internal environment (sap). In this case, there's no net movement of water into or out of the cell because the water potential inside and outside the cell is equal.

In summary: When plant cells neither take nor lose water in water, it signifies that the concentration of solutes in the sap is equal to the concentration of solutes in the surrounding water, leading to an isotonic state.