Which of the following statements is/are true about xylem?

P. Primary cell wall of xylem gives support to the plant. Q. The walls of tracheids are made up of lignin. R. Parenchyma cells of xylem provide mechanical support, defense and water transport.

Correct answer. Xylem is one of the two types of transport tissues in vascular plants. Almost all plant cells produce primary cell walls. The major component of most primary walls in xylem is a disorganised network of cellulose fibrils, which allows the wall to stretch and expand as the cell grows. The secondary wall is deposited on the inner side of the primary wall during and after the cell has elongated or enlarged. The cellulose fibrils in the secondary wall are arranged in a regular fashion with alternating layers at fixed angles to the main axis of the cell. This reinforces the plant cell while preserving the elastic nature of the primary wall. Most of the cell types in xylem can be distinguished based on the shape and features of the secondary cell wall. The walls of tracheids are made up of lignin. Xylem parenchyma cells store water, mineral nutrients and carbohydrates, and respond to wounding. Sclerenchyma cells of xylem provide mechanical support, defense and water transport.