1. Cohesion and Adhesion:
* Cohesion: Water molecules strongly attract each other due to hydrogen bonds. This creates a strong cohesive force that holds water molecules together in long chains, forming a continuous column within the xylem (the plant's vascular tissue for water transport).
* Adhesion: Water molecules also adhere strongly to the hydrophilic (water-loving) walls of the xylem vessels. This adhesion helps pull the water column upwards.
2. Capillary Action:
* The narrow diameter of the xylem vessels, combined with the cohesive and adhesive forces of water, creates capillary action. This phenomenon allows water to rise up the xylem vessels, defying gravity to a certain extent.
3. Transpiration:
* The leaves of trees release water vapor into the atmosphere through tiny pores called stomata. This process, called transpiration, creates a negative pressure (tension) in the xylem. The cohesive forces of water molecules prevent the column from breaking, pulling water upwards from the roots to replace the water lost through transpiration.
4. Root Pressure:
* Roots actively transport minerals from the soil into the xylem. This creates a positive pressure that helps push water upwards in the xylem, especially during the night when transpiration rates are low.
5. Surface Tension:
* The cohesive forces between water molecules create a surface tension on the surface of the water column in the xylem. This tension helps maintain the integrity of the water column and prevents it from breaking.
Together, these properties work in concert to move water from the roots to the leaves of a tree against gravity. This process is essential for the survival of the tree, as it provides water for photosynthesis and other vital functions.
