The protective outer covering of a plant cell is called the cell wall. It is composed primarily of cellulose, providing structural support and protection against mechanical stress. Additionally, the cell wall helps maintain the shape of the cell and regulates transport of substances in and out. Unlike animal cells, plant cells have this rigid layer that contributes to the overall integrity of the plant, allowing it to withstand various environmental conditions. The cell membrane lies just inside the cell wall, further regulating the entry and exit of nutrients and waste products.