How does transpiration creates suction

1. HOW DOES TRANSPIRATION CREATES SUCTION PULL ?

2. Transpiration

3. It is the transfer of water from the plants to the atmosphere. It takes place when stomata opens for gas exchange while photosynthesis . It helps the plants cool down as it absorbs the heat when it evaporates(same principle as that of when we sweat). It also creates suction pull, which leads the water from roots in the xylem rise up. BUT HOW ????????????

4. Before that let us know something about adhesion and cohesion.

5. It is the attraction of two molecules of the different kind. It may be because of bonding . When opposite charges attract each other adhesion may take place. Like the water is clinging to the leaf. Adhesion

6. LIKE … When water is poured on clean glass, it tends to spread, forming a thin, uniform film over the glasses surface. This is because the adhesive forces between water and glass are strong enough to pull the water molecules out of their spherical formation and hold them against the surface of the glass, thus avoiding the repulsion between like molecules .

7. This is the attraction of molecules of same type. The attractive forces exist between molecules of same substance. Water droplets are formed because of cohesive forces. Cohesion

8. Cohesion-tension theory This theory was proposed by an Irish botanist H.H. Dixon and John Joly (in 1894). They said that water is pulled from up, and not pushed from down .There are 2 important things of this theory. They are: Cohesion of water and adhesion between water and xylem tissues Transpirational pull

9. (vapor form) (liquid form) (vapor form)

10. Cohesion of water and adhesion between water and xylem tissues As the water molecules attract each other (by cohesion) they cannot be easily separated away from each other. Further, there is attraction between water molecules and the inner wall of xylem . So , one can determine that water cannot be pulled away because of strong adhesive and cohesive forces between water and xylem and water and water respectively.

11. Now the main thing…….

12. It is the pulling force responsible for lifting the water. As water is lost in form of water vapor to atmosphere from the stomata, there is a negative pressure created in the cells of leaves or it can be said that the concentration of water becomes less(in the leaves). Transpirational pull

13. This negative pressure is gradually transmitted downwards through xylem.

14. NOW, anything moves from an area of lower concentration to an area of higher concentration. And so … the water will also slowly start moving up to equalize the water concentration in the leaves.

15. This is how water is transported to the leaves from the roots through xylem. Like this, water can cover huge distances(upwards) say 50 or 60 feet. Despite of many other theories , this theory is preferred as the best one by the scientists after Dixon also.