Tag: transport of water and minerals

In a typical dicot root; root hairs are present in the zone of cell maturation. Root hairs are unicellular extensions of root epidermis, called as epiblema, which absorb water due to increased surface area for absorption. Zone of cell division, zone of elongation and root cap generally lack root hairs.

When concentration of soil solutes is low then the soil solution is hypotonic as compared to cell sap. Water always flows from a hypotonic solution to a hypertonic solution. Hence, when the soil solution is hypotonic due to low concentration of solutes, the water flows into the cell due to the process of endosmosis and absorption of water is increased.

Water flows from higher water potential to lower water potential. Water potential of pure water is zero. As solutes are dissolved in it, the water potential decreases. More the dissolved solutes, lower will be the water potential. Water potential of all the solutions is always negative. Hence, water flows from higher water potential (i.e., less negative water potential) towards a lower water potential (i.e., more negative water potential). It is clear that absorption of water will occur if water potential of cell sap is lower than pure water and soil solution.

It is wrong to believe that water absorption and absorption of mineral salts are two unrelated processes. In fact the active uptake of ions is partly responsible for the water potential gradient in roots, and therefore for the uptake of water by osmosis. Some ions also move into the epidermal cells passively. Since soil has less concentration of minerals; most of the minerals are absorbed actively.

Roots absorp water from soil through diffusion process. Diffusion occurs in the presence of  concentration gradient. When amount of solute is less in soil solution then amount of water is more in soil solution. In this condition more amount of water will diffuse from soil to roots that's why water absorption is increased.

• The attraction between the molecules of dissimilar substances is termed as adhesion. 
• Walls of tracheid and vessels of xylem are made up of lignin and the cellulose. Hence due to the adhesive force, they have a close affinity for water.
• So, the correct answer is option A.

Water-logging indicates to the concentration of soil with water. When the soil is saturated with water over the course of time leads to blockage of air phases and anaerobic condition is succeeded, now the soil may be regarded as waterlogged. In the intense condition (physiologically dry) continued waterlogging leads to anaerobiosis (life sustaining by organism in the absence of oxygen), mostly occurs to mesophytes roots, denitrification and methanogenesis due to reduced atmosphere. 

Root hair absorbs water from soil through osmosis. Water will be absorbed by root hairs by osmosis as the environment in the soil is hypotonic. This kind of absorption takes place passively. The water can easily move from the region of higher concentration to the low concentration without expenditure of energy. The cell membrane of the root cells acts as a semipermeable membrane. It passes the epidermis, cortex, endodermis, casparian strip and pericycle and protoxylem and metaxylem.