Compare the structure and function of the xylem and phloem

Plants have two separate transport systems. A network of xylem vessels transports water and mineral ions from the roots to all other parts of the plant. Phloem tubes transport food made in the leaves to all other parts of the plant. Neither of these systems has a pump, this is because they are not as active as animals and do not need such rapid supplies of food. Neither xylem nor phloem transports oxygen as oxygen gets to a plants cell by diffusion. Both stems and roots contain xylem vessels and phloem tubes. In a stem these are grouped into vascular bundles arranged in a ring. In a root these are arranged in the centre forming a structure called the stele. Xylem tissue has the dual functions of support and transport. It contains several†¦show more content†¦As water evaporates from the cell walls of mesophyll cells, more water is drawn into them to replace it. The source of this water is the xylem vessels in the leaf. Water constantly moves out of these vessels, down a water potential gradient either into the mesophyll cells or along their cell walls. The removal of water from the top of xylem reduces the hydrostatic pressure. The hydrostatic pressure at the top of the xylem vessel becomes lower than the pressure at the bottom. This pressure difference causes water to move up the xylem vessels, causing a pressure difference between the top and bottom. The water in the xylem vessels is under tension; its walls may collapse inwards as a result of the pressure differences. Xylem vessels have strong lignified walls to stop them from collapsing in this way. The movement of water up through xylem vessels is by mass flow. This means that all the water molecules move together, as a body of liquid. In contrast to the structure of the xylem vessels, the sieve tubes in the phloem have end walls which when next to each other a sieve plate is formed. This is made up of the walls of both elements, perforated by large pores. Companion cells are closely associated with their neighbouring sieve elements. Numerous plasmodesmata pass through their cell walls, making direct contact between the cytoplasms of the companion cell and sieve element. The liquid inside the phloem sieve tubes is called phloem sap containing sucrose,Show MoreRelatedCompare and Contrast Xylem Tissue and Phloem Tissue, Including Their Respective Structures and Functions.888 Words   |  4 PagesCompare and contrast xylem tissue and phloem tissue, including their respective structures and functions. The stems and roots of plants contain two separate transport systems; xylem vessels and phloem tubes, of which neither transport oxygen as it is transported to cells by diffusion. 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