Xylem tissue transports water and mineral ions in solution. These substances move up the plant from the roots to the leaves.
Phloem tissue mainly transports sugars in solution, both up and down the plant.
Xylem and Phloem make up a plant's vascular system. They are found throughout a plant and transport materials to all parts. Where they're found in each part is connected to the xylem's other function - support.
In a root, the xylem is the centre surrounded by phloem to provide support for the root as it pushes through the soil.
In the stems, the xylem and phloem are near the outside to provide a sort of scaffolding that reduces bending.
In a leaf, xylem and phloem make up a network of veins which support the thin leaves.
Xylen is a tissue made frm several different cell types.
Xylem vessels are very long, tube-like structures formed from cells joined end to end.
Xylem has no end walls on these cells, making an uninterrupted tube that allows water to pass up through the middle easily.
Xylem cells are dead, so they contain no cytoplasm.
Xylem walls are thickened with a woody substance called lignin, which helps to support the xylem vessels and stops them from collapsing inwards. The amount of Lignin increases as the cell gets older.
In the xylem water and ions move into and out of vessels through small pits in the walls where there is no lignin.
Phloem tissue transports solutes, mainly sugars like sucrose, round plants.
Like Xylem, Phloem is formed from cells arranged in tubes. But unlike Xylem, it is purely a transport tissue.
Phloem tissue contains phloemfibres, phloemparenchyma, sievetubeelements and companioncells.
Sievetube cells and companion cells are the most important cells types in phloem for transport.
Sieve tube elements are living cells that form the tube for transporting solutes through the plant. They are joined end to end to form seive tubes
The 'sieve' parts are the end walls in the phloem, which have lots of holes in them to allow solutes to pass through.
Sieve tube elements have no nucleus, a very thin layer of cytoplasm and few organelles . The cytoplasm of adjacent cells is connected through the holes in the sieve plates.
The lack of a nucleus and other organelles in sieve tube elements means that they can't survive on their own. So there's a companion cell for every sieve tube element.
Companion cells carry out the living functions for both themselves and thier sieve cells. For example, they provide the energy for the active transport of solutes.