Question

As a plant grows, the stem often becomes thickened and somewhat woody since it is responsible for supporting the upper branches and leaves. Cells in this area of the plant develop

Answer 1

Cells in this area of the plant develop THICKENED CELL WALLS.
Cell wall is a very important cell organelle in plant, it gives rigidity to the plants' cells thus supporting them, it also perform a host of other activities. Thickened cell wall are usually rich in lignin. Thickened cell wall in plants are also called secondary cell wall.

Answer 2

thickened cell walls

Cells in the stem, needed for support, develop thickened cell walls. These specialized cells are called collenchyma cells.