Explain about complex tissue
Answers
The complex tissue consists of more than one type of cells which work together as a unit. Complex tissues help in the transportation of organic material, water, and minerals up and down the plants. That is why it is also known as conducting and vascular tissue. The common types of complex permanent tissue are:
Xylem or wood
Phloem or bast.
Xylem and phloem together form vascular bundles.
Xylem[edit]
Xylem consists of:
Tracheids
Vessel members
Xylem fibres
Xylem parenchyma
Cross section of 2-year-old Tilia Americana, highlighting xylem ray shape and orientation.
Xylem serves as a chief conducting tissue of vascular plants.
It is responsible for the conduction of water and mineral ions/salt. Xylem tissue is organized in a tube-like fashion along the main axes of stems and roots. It consists of a combination of parenchyma cells, fibers, vessels, tracheids, and ray cells. Longer tubes made up of individual cells are vessels tracheids, while vessel members are open at each end. Internally, there may be bars of wall material extending across the open space. These cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at the ends. They do not have end openings such as the vessels. The tracheids end overlap with each other, with pairs of pits present. The pit pairs allow water to pass from cell to cell.
Though most conduction in xylem tissue is vertical, lateral conduction along the diameter of a stem is facilitated via rays.[1] Rays are horizontal rows of long-living parenchyma cells that arise out of the vascular cambium. In trees and other woody plants, rays radiate out from the center of stems and roots and appear like spokes on a wheel in cross section. Rays, unlike vessel members and tracheids, are alive at functional maturity.[2]
Phloem[edit]
Phloem consists of:
Sieve tube
Companion cell
Phloem fibre
Phloem parenchyma.
Phloem is an equally important plant tissue as it also is part of the 'plumbing system' of a plant. Primarily, phloem carries dissolved food substances throughout the plant. This conduction system is composed of sieve-tube member and companion cells, that are without secondary walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually also includes fibers, parenchyma and ray cells. Sieve tubes are formed from sieve-tube members laid end to end. The end walls, unlike vessel members in xylem, do not have openings. The end walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous connections are called sieve plates. In spite of the fact that their cytoplasm is actively involved in the conduction of food materials, sieve-tube members do not have nuclei at maturity. It is the companion cells that are nestled between sieve-tube members that function in some manner bringing about the conduction of food. Sieve-tube members that are alive contain a polymer called callose, a carbohydrate polymer, forming the callus pad/callus, the colourless substance that covers the sieve plate. Callose stays in solution as long as the cell contents are under pressure. Phloem transports food and materials in plants upwards and downwards as required.
Complex Permanent Tissue
The complex permanent tissues are made up of more than one type of cell. They coordinate together to perform the same specialized functions in the plant body. They are classified into two types – Xylem and Phloem
Xylem – The xylem tissue is responsible for the conduction of water and minerals from the roots to the leaves and stem. It also provides support to the plants. It has four elements. They are tracheids, vessels, xylem parenchyma and xylem fibres.
Phloem – This complex permanent tissue helps in the translocation of food that is prepared by photosynthesis in the leaves to various parts of the plant. Phloem consists of four elements. They are sieve tubes, companion cells, phloem fibres and phloem parenchyma.