The plants require water and minerals for the process of photosynthesis. The root hairs are the microscopic outgrowths from the outer layer of the root. These root hairs absorb the water and minerals from the soil through the process of osmosis. The osmosis can be defined as follows: The movement of water or solvent molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane is called the osmosis . The movement of water molecules continues to occur across the membrane until equilibrium is reached. At equilibrium, the water potential on both the side of the membrane is equal.

The process of random movement of individual molecules from a region of higher concentration to a region of lower concentration without semipermeable membrane is called the diffusion. Larger the difference in concentration, more rapid the flow of molecules. Diffusion is more rapid in gases than in liquids. When there is no further movement of molecules, a state of equilibrium is reached, which means that the diffusing substance is evenly distributed. For example the supply of carbon dioxide from atmosphere to the leaves for photosynthesis, and the loss of water from the leaves to the atmosphere.