Question

Which of these is a factor not related to transcriptional pull?
A. Capillarity
B. Adhesion
C. Cohesion
D. Ascent of sap

Answer 1

Transpiration is the evaporative loss of water by plants and it takes place mainly through stomata. The transpiration pull is the biological process which involves the force of pulling which is produced by the xylem tissue for the upward movement of water in the xylem vessels.
Let's discuss the above options and find the correct answer:

Complete answer:
- Capillarity: The capillary action is the capacity of liquid to flow in limited spaces without the help of or in opposition to the external forces like gravity. The water goes to a certain point where it maintains the balanced force of gravity of the column.
- Adhesion: It is the force of attraction which results in the attraction between the water molecules and the xylem which is required for transpiration pull. At the time, when transpiration stops, the water is held in the stem and the leaf by the force of adhesion.
- Cohesion: It is the process of attraction between a similar type of molecules which makes the water molecules attached together when they get lifted by the transpiration pull. The main role of cohesion is to move more water throughout the xylem.
- Ascent of sap: It is the process in the xylem tissue of plants for the upward movement of water and minerals from the roots to the top. This is the force of suction.
Hence, the correct answer is A. Capillary.

Note: The transpiration pull grows a negative tension in the xylem sap which is transferred down to the roots. The mesophyll cells in the leaf which has moist walls lose water vapour by the process transpiration.