The cellular structure responsible for maintaining the shape of plant cells is the cell wall. Composed primarily of cellulose, along with other polysaccharides and proteins, the cell wall provides structural support and protection to the plant. It helps withstand internal pressure from the plant’s central vacuole, ensuring that the cells maintain their shape. In addition to its supportive role, the cell wall is involved in regulating the movement of substances in and out of the cell, thus contributing to homeostasis. It plays a critical role in enabling plants to grow upright and remain rigid.