The ascend of sap in the xylem tissue of plants is the upward movement of water and minerals from the root to the crown. Xylem is a complex tissue consisting of living and non-living cells. The conducting cells in xylem are typically non-living and include, in various groups of plants, vessels members and tracheids.
Transpiration pull or the suction force is the force which aids in drawing the water upward from roots to leaves. In leaves, some amount of water is used for photosynthesis and excess water is released into atmosphere through openings called as stomata.