The central vacuole in a plant cell is responsible for turgor pressure. when the vacuole loses water the cytoplasm "shrinks", when the vacuole gains water the cytoplasm seems to puff up. one structure the plant cell keep is shape no matter how much water is in the vacuole. this is

Cell wall

Explanation:

The cell wall is made up of the cellulose, hemicellulose, and pectin polymer chains that crosslink tighly. These fibers are tough giving the cell wall in plants its inflexibility especially if there are additional molecules embedded in the crosslinks such as lignin. This gives the cells of plant rigidity that are important in the support of a plant. The cell wall also protects the cells of plants from turgor pressure (also needed for support) that would easily lyse an animal cell.

The pores of the cell wall are nonetheless larger than those of the cell membrane hence larger molecules pass through the cell-wall than they would across the cell membrane.