Root hairs function as tiny osmotic systems. Each root hair has a thin permeable cell wall, a semipermeable plasma membrane and an osmotically active cell sap present in the central vacuole. Because of the latter a root hair cell has a water potential of -3 to -8 bars. Water potential of the soil water is -0.1 to -0.3 bars. As a result, soil water passes into the root hair cell through the process of osmosis.