Which of the following helps in ascent of sap?

• Root pressure

• Transpiration

• Capillarity

• All of these

D.

All of these

Water is mainly absorbed by roots which goes upwards so as to replace water loss in transpiration and to be used in photosynthesis. This upward movement of water from roots to leaves through stem against force of gravity is cal led ascent of sap. 

There are many theories in order to understand the ascent of sap. 

1. Root Pressure Theory- Root pressure is developed when rate of absorption is more than rate of transpiration and so water is pushed up in the tracheary elements.
2. Capillary Force Theory- According to this, xylem vessels act as minute capillaries and water rises in these capillaries due to capillary action or surface tension.
3. Transpiration Pull Theory- Due to water loss by transpiration suction pressure is increased and water is absorbed from adjacent xylem vessels of leaves and thus sap in under tension.