Ascent of Sap and its Events - An Overview
The upward movement of water and minerals from roots to different plant parts is called ascent of sap. A number of factors play a role in ascent of sap and it takes places in following steps
Root Pressure: Water from soil enters the root hairs due to osmosis. Root pressure is responsible for movement of water up to the base of the stem.
Capillary Action: Water or any liquid rises in a capillary tube because of physical forces, this phenomenon is called capillary action. In the same way, in stem water rises up to certain height because of capillary action.
Adhesion-cohesion of Water Molecules: Water molecules form a continuous column in the xylem because of forces of adhesion and cohesion among the molecules.
Cohesion: The force of attraction between molecules of water is called cohesion.
Adhesion: The force of attraction between molecules of different substances is called adhesion.Water molecules stick to a xylem because of force of adhesion.
Transpiration Pull: Transpiration through stomata creates vacuum which creates a suction. called transpiration pull. The transpiration pull sucks the water column from the xylem tubes and thus water is able to rise to great heights even in the tallest plants.