Question

Central lumen of which one of the following is obliterated?
(a) Tracheids
(b) Xylem fibres
(c) Vessels
(d) Xylem parenchyma

Answer 1

Hint: Obliterated central lumens are known to be present in sclerenchyma fibres. They are also called wood fibres. They are elongated, terminally tapering and thick-walled dead cells, with lignified secondary walls, narrow lumens and bordered pits.

Complete answer:
Xylem fibres contain obliterated central lumen due to very thick walls. Xylem fibres are the sclerenchyma fibres, seen in association with xylem. Hence, they are also called wood fibres. Xylem fibres are elongated, terminally tapering and thick-walled dead cells, with highly lignified secondary walls, narrow lumens and bordered pits. They develop from the same meristematic tissue from which the other xylem cells develop. They are present both in primary as well as secondary xylem. There are two kinds of xylem fibres, namely fibre Tracheids and libriform fibres.

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.
-Vessels have lignified cell walls. They have a large central cavity. They are long and cylindrical conducting tubes. Their end walls are either perforated or dissolved.
-Xylem parenchyma are thin-walled and non-lignified in the primary xylem but slightly lignified in the secondary xylem.

So, the correct answer is 'Xylem fibres'.

Note:
-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.
-Based on origin, xylem can be classified into primary xylem and secondary xylem. The former develops from procambium during primary growth and the latter develops from vascular cambium during secondary growth.
-Xylem is composed of four kinds of cells, namely tracheids, vessels or trachea, xylem fibres and xylem parenchyma. Of these, xylem parenchyma is living and the others are dead.