The structure that supports and protects plant cells is known as the cell wall. Composed primarily of cellulose, this rigid layer provides shape and defense against mechanical stress and pathogens. Unlike animal cells, which have a flexible plasma membrane, plant cells require this sturdy component to maintain their integrity. The cell wall is crucial for maintaining turgor pressure, which helps plants stay erect. Additionally, it plays a role in regulating the passage of substances in and out of the cell.