Question

What is the fate of primary xylem in a dicot root showing extensive secondary growth?
a) It is retained in the center of the axis
b) It gets crushed
c) May or may not get crushed
d) It gets surrounded by primary phloem.

Answer 1

Hint: The conductive portion of the plant body is formed by xylem, a type of complex permanent tissue. It transports mineral salt and water from the roots to the top of the plant. The xylem produced during primary growth from procambium is known as primary xylem. Protoxylem and metaxylem are included. After the protoxylem, but before the secondary xylem, metaxylem forms.

Complete answer:
Complex tissue is a group of different cell types performing common functions. Xylem and phloem are called complex tissues because all cells which function as a unit have different structural organisations. Xylem is made of four different types of cells: tracheids, vessels, xylems and phloem. Phloem consists of seven tube elements, cell complements, parenchyma phloem and phloem fibres. Conducting water and minerals from roots to top plants is linked to Xylem and the transport of organic food by phloem is responsible.
During the dicot root's auxiliary development:
1. The cells of cambium strips delivered to the inward side separate into secondary xylem components, while those delivered to the outside side separate into secondary phloem.
2. The essential remaining parts have a unique position in the central axis point, but the primary phloem is pushed to the outside and squashed.

In this case, the correct answer is 'A-It is retained in the centre of the axis'.

Note:
Vascular bundles are usually found between the palisade and the spongy regions. The midrib region has the largest vascular bundle. Conjoint, collateral and closed are vascular bundles. A bundle of parenchymatous cells is surrounded by each vascular bundle. Xylem is present in the vascular bundle in the upper epidermis and phloem in the low epidermis. In xylem, the upper epidermis is the protoxylem.