Xylem Sap Movement

Water moves upward through the xylem in plants by a combination of factors:

• Transpiration pull: Water evaporation from leaves creates a negative pressure, pulling water upwards
• Cohesion: Water molecules stick together, forming a continuous water column
• Adhesion: Water molecules adhere to the walls of xylem vessels
• Root pressure: Osmotic pressure in roots pushes water upwards (mainly in small plants)

This process is known as the Cohesion-Tension theory of ascent of sap.