Final answer:
Sclerenchyma cells with thicker cell walls that come in many shapes are called sclereids. They are different from other plant cell types like parenchyma, collenchyma, and xylem cells, as they have secondary cell walls thickened with lignin and are diverse in shape.
Step-by-step explanation:
In sclerenchyma, the cells that have thicker cell walls and come in many shapes are known as sclereids. Unlike collenchyma cells, which have unevenly thickened walls and are alive at maturity, sclerenchyma cells including both fibers and sclereids have secondary cell walls that are thickened with lignin and are often dead at maturity. While fibers are long and slender, sclereids are varied in size and shape, contributing to the gritty texture in pears. Parenchyma cells, which fill most of the inside of a plant, have thinner walls and are living at maturity. Xylem cells, which include tracheids and vessel elements, are specialized for water conduction and also have thick walls but are not as varied in shape as sclereids.