Question

Draw and label structure of xylem vessel.

Answer 1

Hint: xylem is the conducting tissue of vascular plants, responsible for the upward conduction of water and inorganic solutes from roots to leaves, flowers, and fruits. It forms a continuous conducting channel through roots, stems, leaves, flowers, and fruits. Also, it forms the wood and the min bulk of roots and stems of vascular plants provides support to the plant body and serves as a storage tissue. Xylem is composed of four kinds of cells, namely vessels, tracheids, xylem vessels, and xylem parenchyma.

Complete step by step answer:
Xylem vessels are long and cylindrical conducting tubes. Their end walls are either perforated or dissolved. Cells appear circular in cross- section. They lose their protoplast and become dead due to the deposition lignin on their secondary wall. Vessels of primary xylem develop from procambium, while those of secondary xylem develop from vascular cambium. Each cell is short, but due to cell fusion, the tubes become much longer. Vessels may reach up to 10cm longer. but in some cases, they may reach up to 2 m or 6m. A vessel is formed of longitudinal rows of elongated and cylindrical tracheary or conducting cells, called vessel members. They have thick and lignified walls and large lumen. They are joined end to end vertically, forming continuous conducting tubes. The end wall between two successive vessel members is called a perforation plate.

Additional information:
- Tracheids are elongated and tube- like dead cells, with tapering, oval, or rounded ends and hard and thick walls, and without protoplast at maturity.
- Xylem fibers are sclerenchyma fibers, seen as associated with xylem. Hence, they are also called wood fibers.
- Xylem parenchyma present in primary as well as secondary xylem. Cells are thin- walled and non- lignified in primary xylem and lignified in secondary xylem.
- Walls of xylem vessel elements undergo secondary thickening by the deposition of lignin in definite patterns.
- The commonest patterns of thickening are annular, spiral, reticulate, scalariform, and pitted.

Note: Xylem vessels differ from tracheids in having perforation plates. The wall between two successive vessel membranes is called a perforation plate. The perforation plate is the plate-like and porous end wall between adjacent vessel members in a xylem vessel. It is common in some ferns, gymnosperms, and most angiosperms. Perforation plates may be simple or multiple. A simple perforation plate is characteristic of angiosperms. Multiple perforation plates is considered to be a primitive feature.