April 18, 2008
Cell Walls in Microorganisms
Lipid bilayers are relatively weak. Certainly there are stronger forms of these membranes, but as implied by the fluid mosaic model these membranes sacrifice rigidity and strength for the ability to allow proteins to freely disperse within the membrane. A consequence of this is that differences in pressure on the two different sides of the membrane can quickly lead to membrane rupture.
This presents a problem for life, because in order to complete the processes needed many proteins, ions and other molecules are required in a very small space. However, to have all these molecules concentrated within the cell would cause there to be a high osmotic pressure for water to flow into the cell. If the cell is not able to control this water absorption, it will swell to the point where it bursts. In animals, the solution is to keep the cells immersed in a solution that has the same number of osmolites dissolved in it as the cells do. Thus the cell cytoplasm is isoosmotic with the extra-cellular environment.
On the Shoulders of Giants 