AP BIOLOGY

Detailed explanation-1: -Complete answer: Sclerenchyma and tracheid contain lignin as a common structural component. The spaces in the cell wall between cellulose, hemicelluloses and pectin are filled by lignin. It plays a very essential role in providing support to tissues like xylem tracheids, vessel elements and sclereid cells.

Detailed explanation-2: -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-3: -Lignin is an organic substance belonging to a group of aromatic alcohols. It is naturally produced by certain plants (especially woody plants and certain algal species). It is found in the secondary cell walls of plants where it serves as a binder for cellulose fibers and provides stiffness to the cell walls.

Detailed explanation-4: -I) Collenchyma contains lignin in its wall thickenings. II) Collenchyma is found only in aerial primary parts and is absent from the roots. III) Chlorenchyma is parenchyma or collenchyma with chloroplasts in them. IV) Collenchyma does not have intercellular spaces.

Detailed explanation-5: -Hint: Sclerenchyma tissues have dead cells. It provides structural support to the plants. It is found in the cortex of stems. Lignin and cellulose helps to provide them with a strong and rigid appearance.