What are the functions of roots in plants and how these help in the uptake of water and salts?

FUNTIONS:

Functions of roots in plants

Roots perform the following functions in plants:

         i.            These anchor the plants in soil.

       ii.            These absorb water and salts from soil.

      iii.            These provide conducting tissues for disturbing these substances to the tissues of the stem.

For better understanding of uptake of water and salts, the internal structure of root should be taken into account.

Anatomy of Root

The centre of the root in most of the cases is occupied by vascular tissue, The xylem composed of conducting elements, the Tracheids and vessels occupies the centre of the root is continuous with the xylem tissues in the stem. The phloem tissue is closely associated to the xylem tissue. The xylem and phloem elements are surrounded by layer of living cells,, the Pericycle. The vascular tissue and the epicycle form a tube of conducting cells called stele. Just outside the stele is a layer of cells called endodermis. This endodermis acts as watertight jacket around the conducting vascular elements because water with its dissolved substances cannot pass around the endodermal cells via their walls.

Outside the endodermis, several layer of large thin walled living cells with intercellular spaces among them are present. This is called as cortex. The air spaces form interconnected air channels necessary for internal aeration. The cell wall of cortical cells are highly permeable to water and its dissolved solutes. The cortex is surrounded by a layer of almost flattened cells. It is epidermis. Some epidermal cells develop long projections called root hairs that extend out among the soil particles around the root. The root hairs increase soil-root contact and enhance water absorption and the volume of soil penetrated.

Uptake of Water and Salt

Root hairs provide large surface area for absorption. The cytoplasm of the root hairs has higher concentration of salts than the soil water, so water moves by osmosis into the root hairs. Salts also enter root hairs by diffusion or active transport. After their entry into the root hairs, water and salts must move through the epidermis and cortex of the root and then into the xylem tissue in the centre of the root.