The soil is the richest source of raw materials for the plant like nitrogen, phosphorous, water and other minerals. Water is essential for all physiological activities of the plant. The absorption of all these substances occurs through a part of the plant called roots.
Water from the soil first goes to the roots. Plant roots cannot pump water itself but they actively transfer nutrient ions to the low parts of a vascular structure which is continuous with a structure called xylem. Xylem consists of long, dead plant cells that form upright tubes. Water flows after the ions.
The plant transport system moves raw materials from roots and energy from leaves. This is done by two independent conducting tubes called xylem which transports water and minerals from the soil and phloem transports the food from leaves to other parts of plants. vessels tracheids of xylem tissue, stem, leaves, and roots form a continuous water conducting channel reaching to all parts of the plant. The difference of concentration of ions in roots and soil, help water to enter roots from the soil to eliminate this difference(caused by root cells take up ions from soil). This maintains the steady movement of water upwards via roots.
the pressure of the absorbed water from the roots make the water to move upward. but this pressure is still not so affective to move it to the top. to move minerals n water to the top, transpiration is used. during transpiration, water loses from the leaves which creates a low pressure of water. which in turn pulls the water upward.