Absorption of Water by Roots from Soil

Once a root hair is in contact with capillary soil water, getting that water into the living cytoplasm of the cell is not a single step but a short sequence of three distinct physical processes, each one handing the water a little further inward: first imbibition, in which the hydrophilic materials of the root-hair wall soak up water; then diffusion, which carries that water across the freely permeable wall to the boundary of the plasma membrane; and finally osmosis, which draws the water through the selectively permeable membrane into the cytoplasm proper. Each of these three processes is driven by its own kind of concentration or pressure difference, and each is examined individually in the sections that follow, but it is their strict order — imbibition, then diffusion, then osmosis — that actually accounts for how soil water ends up inside a living root-hair cell.