Question

Centripetal xylem is the characteristic of
(a) Roots
(b) Stems
(c) Leaf
(d) Petiole

Answer 1

Hint: Such type of xylem develops in a direction from outside to inside and is present in those parts of the plant that are positively geotropic. These parts provide anchorage to the plant and help in getting water and minerals.

Complete answer:
When xylem develops in such a way that the protoxylem lies towards the periphery while the metaxylem lies towards the center, the xylem is termed to be exarch or centripetal. This type of xylem development is seen particularly in the roots of the vascular plants.

The word centripetal means tending to move towards the center. In the exarch condition, the progression of xylem occurs towards the center. Vascular plants can have more than one strand of primary xylem in their stem or root. The two types of primary xylem are protoxylem and metaxylem. Protoxylem is the first developed primary xylem and metaxylem is formed later from the primary xylem. The arrangement of protoxylem and the metaxylem differs between various plant species and defines the particular pattern which is characteristic to certain parts of the plant. The arrangement of protoxylem in the peripheral region and the arrangement of metaxylem towards the central region is called an exarch. In other words, if the maturation/development of xylem is towards the center, it is known as centripetal or exarch xylem.

So, the correct answer is, ‘Roots’.

Note: Apart from the exarch system, other patterns of protoxylem and metaxylem arrangement exist in various plant parts. The arrangement of protoxylem toward the center and the metaxylem towards the periphery is known as endarch xylem. It is also called centrifugal xylem. It is commonly observed in the stem. Additionally, the development of exarch, as well as endarch xylem, is formed, then the xylem is said to be mesarch xylem.