Plant cells, in addition to the plasma membrane, have another rigid outer covering called the cell wall. It lies outside the plasma membrane. It is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants. When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.Functions of cell wall:\xa0i. It permits the plant cell to become turgid.ii. It provides mechanical strength to support the cell.iii. It is freely permeable to water and substances in solution.iv. Cell wall permits the cells of plants, fungi and bacteria to withstand very dilute (hypotonic) external media without bursting.\xa0