NEET BIOLOGY

Detailed explanation-1: -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.

Detailed explanation-2: -In woody plants secondary xylem comprises the bulk of the tissue in the stems and roots. It is the most important supporting tissue in arborescent dicotyledons and most gymnosperms, and the major tissue for the transport of water and essential minerals in woody plants.

Detailed explanation-3: -Wood is the secondary xylem produced by coniferous gymnosperms (conifers) and by dicotyledonous angiosperms (flowering plants). Wood performs two main physiological functions: it conducts water from the roots to the leaves and it supports the branches and crown of trees and shrubs.

Detailed explanation-4: -The cells of the vascular cambium divide and form secondary xylem (tracheids and vessel elements) to the inside, and secondary phloem (sieve elements and companion cells) to the outside. The cells of the secondary xylem contain lignin, the primary component of wood, which provides hardiness and strength.

Detailed explanation-5: -The vascular cambium arises between the primary xylem and phloem of a young stem or root. Parenchymatous cells become meristematic and begin to produce secondary xylem or wood toward the inside of the cambium and secondary phloem toward the outside of the cambium.