The upward movement of water in plants

• Water transport occurs in a plant's xylem tissue & moves upward through a plant through xylem tissue.
• The fluid mixture of materials flowing through the xylem is called sap.  

• Diffusion, transpiration and capillary action must occur together in order to move the upward through plant.

1. Diffusion 

• Plant roots absorb water from the soil through diffusion or osmosis.
• The roots (higher salt concentration). The water flows from the low salt side to the high salt side to the concentration equal.
• The membrane is semi-permeable but if the salt concentration inside the root becomes too low, it will actively transport salt into roots. 

2. Capillary action

• Water molecules have a strong attraction to each other causing the molecules to stick together.
• They also adhere to the surface of the xylem.
• As the plant transpires, water molecule evaporates, pulling another water molecule up through the xylem.
• The water sticks to the side of the xylem and not fall back down.

Cohesion force: The ability of molecules of the same kind to stick together. Water molecules are polar, having positive and negative sides, which causes their cohesion.

Adhesion force: The tendency of molecules different kinds to stick together. Water sticks to the cellulose molecule in the walls of xylem, the force gravity give rise of water within xylem.

3. Transpiration 

• Plants lose water through the leaf surface and stomata involves transpiration.
• Plants lose water through the leaf surface from the stomata or pores in the leaf surface used for respiration and photosynthesis.