Xylem in plants helps in the transportation of water and minerals from roots to leaves.
Cohesion tension theory says that the movement of water in the upwards direction against gravity is guided by the attractive forces between the particles of water which is known as cohesion and thus gives rise to surface tension which pulls the water upwards from the root through the xylem, and this is aided by Transpiration pull and capillary action of water. This is the main mechanism of transport of water in plants. Transpiration pull causes a suction effect on the water column, and water rises, aided by its capillary action. Cohesion (with other water molecules) and adhesion (with the walls of xylem vessels) helps in a continuous flow of water without breaking the column.