The cell wall of a plant cell is made up of insoluble cellulose fibres which are embedded in a matrix of pectin and other materials. The fibres are very strong and often arranged in layers in which they are orientated in different directions. The composite structure provides an extreme resistance from the extension or the compression of the cell. For instance when too much water is taken up, the cell wall prevents the cell from expanding too far and bursting by allowing the cell to become turgid. However the cell wall is completely permeable and thus it has no role in controlling what can enter or leave the cell. [Mary Jones & Geoff Jones, Student Support Materials for Edexcel, AS...