AP BIOLOGY

Detailed explanation-1: -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-2: -Duramen-The central or inner dark coloured non-functional wood or secondary xylem, not takes part in the conduction of water is called Duramen or Heartwood.

Detailed explanation-3: -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-4: -Such modified and non-functional wood is called heartwood. Hence, the correct answer is ‘Heartwood’.

Detailed explanation-5: -Secondary xylem is composed of tracheary elements, rays, fibres, and interspersed axial parenchyma cells. The tracheary elements consist of only tracheids, as in the few vessel-less angiosperms (e.g., Winteraceae), or of both tracheids and vessel elements, as in the vast majority of angiosperms.