Write a note on ascent of sap .

Explanation

the upward movement of water and minerals from roots to different plant parts is called ascent of sap .A number of factors play a role in ascent of sap and it takes places in folowing steps :
(I ) Root pressure : water from soil enters the root hairs due to osmosis .Roots pressure is responsible for movement of water up to the base of the stem .
(ii ) Capillary action : water or any liquid rises in a capillary tube because of physical forces , this phenomenon is called capillary action .In the same way , in stem water rises up to certain height because of capillary action .
(iii ) Adhesion - cohesion of water molecules : water molecules form a continous column in the xylem because of forces of adhesion and cohesion among the molecules .
(iv ) Cohesion : The force of attraction between molecules of water is called cohesion .
(v ) Adhesion : the force of attraction between molecules of different substances is called adhesion . Water molecules stick to a xylem because of force of adhesion .