Question

Most accepted theory of ascent of sap is
A. Capillarity theory
B. Root pressure theory
C. Pulsation theory
D. Transpiration pull theory

Answer 1

Generally ascent sap in the xylem tissue of plants is the upward movement and minerals from the root to crown This process takes place through the xylem’s tracheary element. And theory is also said as cohesion-tension theory.

Complete answer
Ascent of sap is the upper sap movement through the stem. In another way, it can also explain as the method of translocating sap from the roots to the top of the plant is named as the ascent of sap. Let us clarify it briefly, the water is distributed to all parts of the plant after being absorbed by the roots (the abundance of which is wasted by transpiration). The water has to pass upward through the stem to enter the topmost sections of the plant. This upward water movement is called Sap Ascent. Ascent of sap can be analysed under two headings and they are Path of Ascent of Sap and Mechanism of Ascent of Sap.
Now, let us find the solution from the options-

Cohesive force or transpiration pull or the principle of cohesion-tension is the most common theory.
The ascent of xylem sap powered by transpiration mainly depends on the three physical properties of water.
These three properties are cohesion, adhesion, and surface tension.

Thus, the correct answer is option (D) Transpiration pull theory.

Note: A transpiration pull can be described simply as a biological process where the pulling force is generated within the xylem tissue. This force assists in pushing water upward through the xylem vessels. In this process, water loss is observed through leaves in the form of vapours.