The correct answer is option 4, Osmosis. Osmosis is the process by which water molecules move from an area of higher water concentration to an area of lower water concentration across a semi-permeable membrane, such as the root hairs of plants. Root hairs are elongated outgrowths of the root epidermis and they significantly increase the surface area for water absorption. These structures are in close contact with the soil particles, where water is present in higher concentration. The root hairs create a gradient that allows water to pass through their cell walls and cell membranes into the root tissue through osmosis. This movement of water is essential for the uptake of nutrients dissolved in the soil water by the roots, which is then transported throughout the plant.