Final answer:
Sclerenchyma cell walls are impregnated with lignin, which provides rigidity and support to plants. Lignin makes plant tissues woody and is resistant to degradation, contributing to the evolutionary success of plants.
Step-by-step explanation:
Sclerenchyma cells have rigid cell walls that are impregnated with lignin, an organic polymer. These cells provide support to the plant and are characterized by having a secondary cell wall that is thickened with deposits of lignin. There are two main types of sclerenchyma cells: fibers, which are long and slender, and sclereids, which are smaller in size and give pears their gritty texture. Lignin is critical in making plant tissues rigid and woody, enabling plants to grow tall and resist the force of gravity. Furthermore, due to its complexity and resistance to degradation, lignin contributes to the longevity of plants and their evolutionary success.