Transport in Plants Question 27
27. The rupture and fractionation do not usually occur in the water column in vessel/ tracheids during the ascent of sap because of
[2008]
(a)
lignified thick walls
(b) cohesion and adhesion
(c) weak gravitational pull
(d) transpiration pull
Show Answer
Answer : b
Hints & Solutions
(b) Rupture and fractionation do not usually occur in the water column in vessel/ tracheids during the ascent of sap because of cohesion and tension. The water molecules have a great mutual attraction to each other or tremendous cohesive power which is sometimes as much as 350 atmospheres. Thus, the transpiration pull develops a negative pressure in the uppermost xylem cells. It is transmitted from there into the xylem of stems, and then to the roots.
