Question

Explain the following forces in terms of the role they each play in the ascent of xylem sap:

1. role of negative pressure for water potential differences

2. adhesion  

3. cohesion

Answer 1

Answer :

Hydrostatic pressure generated in root which forces the water upward in the semis the root pressure. Negative pressure or pull or suction is created in the leaves as a result of transpirational pulls the water moves upward.

Cohesion and adhesion of water molecules creates pressure that is 350 atm which is responsible for conducting water to the stem in great heights without breaking the water column.

The attraction between the water molecules and the cell wall of the xylem cells is called adhesion. The water molecules remains adhere to the xylem tissues so the column of water does not break. So adhesion helps the water molecules to creep tip.

The force of the attraction among water molecule is called cohesion. It forms solid chain if water molecules like a column within the xylem tissue.

Cohesion adhesion tension mechanism is must prominent mechanisms in ascent of sap in xylem