Question

Sap ascends in woody stem, because of

• A. Transpiration pull
• B. Capillarity
• C. Molecular adhesion
• D. Photosynthesis

Answer 1

Answer: (A)

Transpiration pull

The most widely accepted theory of ascent of sap is transpiration pull cohesion-tension theory. According to this theory, transpiration loss of water generates tension or transpiration pull. The tension is the pulling force, which lifts water to great heights in woody trunks of giant angiosperm and gymnosperm trees. In the xylem elements is maintained a continuous water column due to cohesion force of water molecules with each other and adhesion force with the xylem elements. Thus, the ascent of sap is a passive physical process.

So, the correct answer is option A.