NEET BIOLOGY

Detailed explanation-1: -Lignin provides mechanical strength and resistance against pathogens, and makes the cell walls impermeable to water, thus enabling the transport of solutes via tracheids in the xylem tissue.

Detailed explanation-2: -Xylem or wood is the major tissue of higher vascular land plants and exhibits a porous structure which is primarily composed of cellulose, other structural polysaccharides and lignin.

Detailed explanation-3: -The xylem is composed of nonliving cells (tracheids and vessel elements) that are stiffened by the presence of lignin, a hardening substance that reinforces the cellulose cell wall. The living sieve elements that comprise the phloem are not lignified.

Detailed explanation-4: -The lignin adds compressive strength and stiffness to the plant cell wall and is believed to have played a role in the evolution of terrestrial plants by helping them withstand the compressive forces of gravity. Lignin also waterproofs the cell wall, facilitating the upward transport of water in xylem tissues.