AP BIOLOGY

Detailed explanation-1: -Lignin is the complex phenolic polymer that strengthens the secondary cell wall of xylem cells, such as water-conducting tracheary elements and supportive fibers, and is most evident in woody tissues of trees.

Detailed explanation-2: -The pit membrane, which lies in the center of each pit, allows water to pass between xylem conduits but limits the spread of embolism and vascular pathogens in the xylem.

Detailed explanation-3: -Xylem is a tissue consisting of dead, hollowed-out cells that form a system of pipes. The walls of xylem cells are lignified (strengthened with a substance called lignin ). This allows the xylem to withstand pressure changes as water moves through the plant.

Detailed explanation-4: -Lignin helps in the transportation of water in stems. Hence, it is present in xylem cells, that’s why they are heavily lignified and make up the wood of woody plants.