The structure responsible for maintaining the shape of a plant cell is the cell wall. The cell wall is a rigid outer layer composed mainly of cellulose, providing structural support and protection to the cell. This feature is unique to plant cells, allowing them to maintain turgor pressure from the surrounding environment and resist internal pressure. The cell wall also plays a role in regulating substance movement in and out of the cell, contributing to overall cell function. By giving cells their shape, the cell wall helps ensure proper growth and development in plants.