A very important part of plant cells is located outside the cells themselves: plant cell walls. Composed of numerous different building blocks (mostly polysaccharides, but also proteins and, particularly in cells that contribute to structural strength, lignin's), cell walls determine the shape of the cells and provide a counterforce to the osmotically generated turgor pressure. In this lecture we look at the major polysaccharides that are found in the middle lamella, primary wall, and secondary wall, and a very simplified model of how we think the plant cell wall is organised. The role of lignin's as structural and water-proofing material is discussed briefly. Copyright 2012 La Trobe University, all rights reserved. Contact for permissions.