Root hair cells are found near the tips of roots. Each one has a long, thin extension called a root hair that grows out between the soil particles. This gives the cell a very large surface area, so more water and mineral ions can be absorbed.
Water enters the cell by osmosis. The soil water is dilute and the cell sap inside the large vacuole is more concentrated, so water moves into the cell through the partially permeable membrane. The root hair and the thin cell wall mean water has only a short distance to travel.
Mineral ions such as nitrate are usually at a lower concentration in the soil than in the cell. They are absorbed by active transport, which moves them against the concentration gradient and needs energy from respiration. This is why root hair cells contain many mitochondria. They have no chloroplasts, because there is no light underground.
