What sclerenchyma is
The second strengthening tissue takes the thickening as far as it will go — and the cells do not survive it.
Sclerenchyma
Sclerenchyma tissue contributes rigidity and mechanical strength to the plant body. Its cells are dead.
The characteristics
- They are dead cells.
- Lignin has been deposited on the cellulose cell walls.
- The cell walls are uniformly thickened, leaving a hollow space in the middle of the cell.
- The cells are tightly packed, so there are no intercellular spaces.
Lignin
Every plant cell wall you have met so far was cellulose. Lignin is a second substance, laid down on top of the cellulose, and it is what makes wood woody. It is far harder than cellulose and it is waterproof — which is where the trouble starts for the cell inside.
The thickening is what kills the cell
Once lignin coats the wall all the way round, water and dissolved substances can no longer reach the living contents. The cytoplasm dies and the cell is left as an empty box with very strong walls. The plant does not lose anything by this: what it wanted was the box.
You already knew the cell wall was non-living
Grade 10 said outright that the plant cell wall is non-living. Sclerenchyma is that fact taken to its conclusion — a tissue in which nothing is left but the wall, and which goes on holding the plant up for as long as the plant stands. The trunk of a tree is mostly cells that died years ago.