Root hair, or absorbent hairs, are outgrowths of epidermal cells, specialized cells at the tip of a plant root. They are lateral extensions of a single cell and are only rarely branched. They are found in the region of maturation, of the root. Root hair cells improve plant water absorption by increasing root surface area to volume ratio which allows the root hair cell to take in more water. The large vacuole inside root hair cells makes this intake much more efficient. Root hairs are also important for nutrient uptake as they are main interface between plants and mycorrhizal fungi. Function The function all root hairs is to collect water and mineral nutrients in the soil to be sent throughout the plant. In roots, most water absorption happens through the root hairs. The length of root hairs allows them to penetrate between soil particles and prevents harmful bacterial organisms from entering the plant through the xylem vessels. Increasing the surface area of these hairs makes plants more efficient in absorbing nutrients and interacting with microbes. As root hair cells do not carry out photosynthesis, they do not contain chloroplasts. Importance Root hairs form an important surface as they are needed to absorb most of the water and nutrients needed for the plant. They are also directly involved in the formation of root nodules in legume plants. The root hairs curl around the bacteria, which allows for the formation of an infection thread into the dividing cortical cells to form the nodule. Having a large surface area, the active uptake of water and minerals through root hairs is highly efficient. Root hair cells also secrete acids (e.g., malic and citric acid), which solubilize minerals by changing their oxidation state, making the ions easier to absorb. Formation Root hair cells vary between 15 and 17 micrometers in diameter, and 80 and 1,500 micrometers in length. Root hairs are found only in the zone of maturation, also called the zone of differentiation. They are not found in the zone of elongation, possibly because older root hairs are sheared off as the root elongates and moves through the soil. Root hairs grow quickly, at least 1 μm/min, making them particularly useful for research on cell expansion. Just prior to and during root hair cell development, there is elevated phosphorylase activity. Fungal interaction Root hairs are essential for healthy plant nutrition, especially through their interactions