What carbohydrate material lines the xylem vessels and provides strength and support?

Lignin is the correct answer because it is a complex organic polymer that is deposited in the cell walls of vascular plants, particularly in the xylem. This provides crucial structural support and strength, allowing plants to withstand the pressures of gravity and water transport. Lignin reinforces the walls of xylem vessels, making them rigid and enabling them to efficiently conduct water from the roots to the rest of the plant.

While cellulose is a major component of cell walls, it primarily provides flexibility and is not specifically associated with the xylem's support structure. Pectin serves to bind cells together and contributes to cell wall integrity but does not impart the same level of strength as lignin. Chitin, found in the exoskeletons of arthropods and cell walls of fungi, is not present in vascular plants and thus is not relevant to xylem structure. These differences highlight why lignin is essential for the function of xylem vessels in plants.