Question

Explain how water is taken up by the plant roots and transported throughout the plant. Show the pathways and explain the mechanisms used to reach all parts of the plant.

Answer 1

The movement of plants from water to land resulted in the development of internal mechanisms to supply all the parts of the plant with water. The Plant has Vasular Tissues , tracheophytes. These developed complex vascular systems that move nutrients and water throughout the plant body through "tubes" of conductive cells. The vascular tissues of these plants are called xylem and phloem. The xylem of vascular plants consists of dead cells placed end to end that form tunnels through which water and minerals move upward from the roots to the rest of the plant. Phloem, which is made up of living cells, carries the products of photosynthesis( i.e food of plants) from the leaves to the other parts. The vascular system is continuous throughout the whole plant, even though the xylem and phloem are often arranged differently in the root than they are in the shoot.

The major mechanism by which water along with dissolved minerals is carried upward through the xylem is called TATC (Transpiration-Adhesion-Tension-Cohesion). In this transpiration, the evaporation of water from the leaf, is theorized to create a pressure differential that pulls fluids held together by cohesion up from the roots.

Water transport also occurs at the cellular level, as individual cells absorb and release water, and pass it along to neighboring cells. Water enters and leaves cells through osmosis, the passive diffusion of water across a membrane. In plants, water always moves from an area of higher water potential to an area of lower water potential. Water potential results from the differences in osmotic concentration, the concentration of solute in the water as well as differences in water pressure caused by the presence of rigid cell walls between two regions. The relationship between the amount of dissolves solute and water potential is inverse : where there is a lot of dissolved solute the water potential is low.

Most of the water that a plant takes in enters through the root hairs. The water diffuses osmotically into the root hairs because the concentration of dissolved materials in the plant's cellular cytoplasm is high.In the Root Hairs, there are two pathways through which water travels from the outside of the root to the core, where it is picked up by the xylem. The first of these pathways is the symplast, in which water moves across the root hair membrane and through the cells themselves, via channels that connect their contents. An alternate route for water is the apoplast, in which water travels along cell walls and through intercellular spaces to reach the core of the root. Once in the xylem, the water can be carried by TATC to all the other parts of the plant.

Thus overall , water transportation occurs in the plant through the combined efforts of individual cells and the conductive tissues.