Question

Secondary xylem is
a. Endarch
b. Exarch
c. Mesarc
d. None of the above

Answer 1

Hint: Xylem is a vascular tissue responsible for the conduction of water and nutrients from the roots to the shoots and leaves. Based on the stage and growth, a xylem is classified as primary xylem and secondary xylem.

Complete Answer:
The complex tissues are made of more than one type cells which work together as a unit. Xylem and phloem constitute the complex tissues in plants.

Primary xylem: The first formed primary xylem elements are called protoxylem and later formed primary xylem is called metaxylem. Types of primary xylem
- Endarch: In this type of primary xylem, the protoxylem lies towards the centre and metaxylem lies towards the periphery of the organ.
- Exarch: In this type of primary xylem, the protoxylem lies towards the periphery and metaxylem lies towards the centre.
- Cnetrarch: In this type of primary xylem, there is one vascular strand and protoxylem is located at the centre surrounded by metaxylem.
- Mesarch: In this type of primary xylem, there are several vascular strands and protoxylem is located in the centre surrounded by metaxylem.

Secondary xylem: It is a type of xylem formed from the secondary growth. Secondary xylem is associated with lateral growth rather than vertical growth as in primary xylem.

Therefore the correct answer is (d) None of the above, as the rest of the options belong to primary xylem.

Note: The primary xylem comes from the procambium whereas secondary xylem grows from the vascular cambium. Secondary xylem is absent in non-woody plants but is present in trees and shrubs.Its cell walls are thickened by the deposition of lignin,thereby providing mechanical support to such plants.