AP BIOLOGY

Detailed explanation-1: -Xylem helps in transportation of water. The cell wall of cells making up the xylem contains lignin. This lignin is water resistant and provides mechanical support to the xylem.

Detailed explanation-2: -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-3: -Both lignin and cellulose are found in the rigid cell walls of the xylem cells (those that conduct water) in the primitive plant Selaginella.

Detailed explanation-4: -Sclerenchyma tissue, when mature, is composed of dead cells that have heavily thickened walls containing lignin and a high cellulose content (60%–80%), and serves the function of providing structural support in plants.

Detailed explanation-5: -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.