Why do some root cell have root hair

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. ... Having a large surface area, the active uptake of water and minerals through root hairs is highly efficient.

Explanation:

Root hairs appear when the epidermis differentiates. The epidermis has specialized cells that are root hair cells. Much attention has been given to root hairs because of their presumed importance as absorbing surfaces.

when it is at an intermediate population density