Question

Which of the following theory gave the most satisfactory explanation for the ascent of sap?

• A. Relay pump theory
• B. Transpirational pull theory
• C. Root pressure theory
• D. None of the above

Answer 1

The correct option is B Transpirational pull theory

The transpiration pull theory is the most accepted theory for the ascent of sap. Dixon and Jolly gave transpiration pull theory. According to this theory, the ascent of sap in plants is a passive physical process, which occurs under the influence of transpiration pull generated due to loss of water from aerial parts. The water lost from the leaves creates a high solute potential and reduces water potential. The reduced water potential creates a suction pull and allows ascent of sap. Other than the pull, a continuous column of water is also essential for the rise of water in xylem elements. The continuous column of water is maintained by cohesion forces between water molecules and adhesive forces between water molecules and vascular elements of the plant.

Thus, the correct answer is option B.