The function of a cell wall has the same function of the cell membrane; it protects the cell. Cell wall is made up of cellulose that is only present in plant cells. Cellulose is a sugar that has a sheet like structural carbohydrate. It is rigid that is used for support and provides protection to the plant cell from damage. They cannot be dissolved in water. An example is if you eat food that contains mostly of leaves. You will observe that you will eliminate the same material as when you it. That is because our human body does not have the enzyme that dissolves the cellulose.