Question

Centripetal and centrifugal xylem are the important features of
A. Root and stem respectively
B. Exarch and endarch respectively
C. Endarch and exarch respectively
D. Both 1 and 2

Answer 1

Hint: Growth from outside to inside is centripetal whereas the growth from inside to outside is centrifugal. Protoxylem and metaxylem’s orientation will help us to understand the answer to this question. Metaxylem is the part of xylem that is formed after the protoxylem and also gets differentiated after the protoxylem.

Complete answer: Xylem is a specialised tissue of vascular plants that transports water and nutrients from the plant (soil) to the stems and leaves. It provides mechanical support and storage. The water-conducting function of xylem is one of the distinguishing features of vascular plants.
The xylem of vascular bundles is differentiated in protoxylem and metaxylem based on the structural and functional difference of their elements.
In the xylem, the protoxylem and metaxylem vessels show orientation about the central axis. On this basis, there are two types of arrangements in the xylem: centripetal and centrifugal.
The centripetal arrangement is when the younger metaxylem vessels are found towards the pith and the older protoxylem vessels are away from the pith. This condition is featured as Exarch.
In the centrifugal arrangement, the older protoxylem vessels are found towards the pith but the younger metaxylem vessels are found away from the pith. This condition is featured as Endarch.

So the answer is option B: exarch and endarch respectively.

Note: Exarch is used when there is more than one strand of primary xylem in the root or stems developing from outside to inside featuring centripetal.
Endarch is used when there is more than one strand of primary xylem in the root or stems developing from inside to outside featuring centrifugal.