Because you will be working with potato cells in the laboratory, you need to understand the concept of water potential. Biologists use this term to describe the tendency of water to leave one place in favor of another. Water always moves from an area of higher water potential to an area of lower water potential.
Water potential is affected by two factors: pressure and the amount of solute. For example, imagine a red blood cell dropped into distilled water. Water will move into the red blood cell and cause the cell to expand, stretching the flexible membrane. At some point, the pressure of the incoming water will cause the cell to pop, just like an over-filled balloon.
Why don't red blood cells pop in the bloodstream?
If a plant cell is placed in distilled water, water will enter the cell and the cell contents will expand. However, the elastic cell wall exerts a back pressure, which will limit the net gain of water.