Concept: Secondary thickening in plant cells often involves highly rigid, impermeable polymers that restrict nutrient flow, leading to programmed cell death.

Solution: Lignin is deposited in the secondary cell walls of specialized plant cells (like xylem vessels and sclerenchyma). It is highly impermeable and tough. Once fully lignified, the cell loses its protoplasm and becomes structurally dead, functioning only as a mechanical support or water pipe.

Distractor Autopsy: Cellulose and chitin allow for a living, metabolically active cell to exist within.