I’ve been thinking a lot about roots lately – welcome to my mind and its strange obsessions! (FYI, the next post will explain where this obsession started). So I wanted to start a series of post by writing about the part of the root that brings water from the soil into the tissue of a plant.
Everyone knows that roots absorb water but many probably don’t realize that there’s a special part of the root that generally makes this water absorption possible. Without these unique cells, most plants wouldn’t be able to survive. The cells I’m talking about are root hairs.
The very tip of a root is covered by a root cap, a mass of cells that protect the growing part of the root and aids in allowing the root to push through the soil. Directly behind the root cap is the apical meristem, the area where new, undifferentiated cells are formed. This is the area of cell division.
Behind the area of cell division is the zone of cell elongation in the root. Just as the name implies, this is the part of the root where the cells elongate and grow. Behind this zone is the zone of maturation. Here the cells mature and take on the function that they’ll have throughout the life of the root.
In the zone of maturation, some of the epidermis cells – those making up the exterior of the root – elongate and give the root the appearance of being covered with fuzz or hairs. These are the root hairs.
Each root hair is a single cell that only lives for a short time. The purpose of them is to increase the surface area of the root so that it has more contact with the soil and can better absorb water. The area of the root that has root hairs is only about 1/4 of an inch long and occurs right behind the growing tip. All of those root hairs increase the surface area of the root by more than 100 fold.
As the root grows, that 1/4 inch zone of root hairs continues to develop right behind the growing tip of the root. Older root hairs die as the root grows. For a plant to have good water absorption, the roots need to continually be growing and producing new root hairs.
The mechanisms of how water is absorbed by the root hairs and moves into the plant are very complex, involving water potentials, active absorption, passive absorption and a host of other processes. It’s enough to know that the vast majority of absorption of water occurs within the root’s zone of maturation and is a result of the presence of root hairs.
I think this is pretty amazing. Every plant that you have (with a few exceptions), whether growing in the yard or in a pot, has to be continually growing new roots with new root hairs in order for the plant to absorb water. Beneath the surface of the soil, roots are growing, old root hairs are dying and new root hairs are forming, all for the purpose of keeping the plant’s cells hydrated.