NEET BIOLOGY

Detailed explanation-1: -In old trees, the central dark region is called the heartwood. It consists of non conducting elements of xylem (vessels) with heavy deposition of lignin, invaded by tyloses, deposition of secondary metabolites like resins, tannins etc. So, the correct answer is ‘heartwood’

Detailed explanation-2: -(iii) Sapwood is the central, dark coloured, non-conducting part of secondary xylem.

Detailed explanation-3: -Solution : Heartwood (duramen) is the central wood of an old stem. It is dark coloured part of secondary xylem.

Detailed explanation-4: -The deposition of organic substances like resins, oils, tannins, gums, etc. in the innermost layers of the stem gives the secondary xylem, a dark brown color appearance. Depositions of these substances make them hard, durable, and resistant to the attacks of microorganisms.

Detailed explanation-5: -The heartwood is located at the inner part (center) of the wood. It is called as such because of being located at the center of the wood.