D1 Analyse the role of the phospholipid bilayer in terms of the movement of materials in and out of cells: The phospholipid bilayer has two layers of phospholipid molecules, which form a barrier around the contents of a cell. Once the phospholipid bilayer is formed it is then able to contain proteins, ions and other molecules that are required to prevent them from diffusing. The phospholipid tails points inwards, facing each other, which allow them to form a non-polar hydrophobic interior. Some of the phospholipid tails can be either unsaturated or saturated, although if there are more tails that are unsaturated will mean that there will be more fluid within the membrane. This is because an unsaturated tail contains fatty acids, which means they fit together loosely. The phospholipid heads outwards and they surround the outer layer of the cell membrane.
The main function of the phospholipid bilayer is to provide the cell membrane with structure and also act as a barrier when movement is taking place. Depending on the fluidity of the cell membrane will depend on how smoothly constituents move through in and out of the cell. The fluidity of a membrane is influenced by the composition of phospholipid tail group’s, cholesterol levels and temperature. Cholesterol also has a hydrophilic head and a hydrophobic tail and fits between the phospholipid molecules. It helps regulate the levels of fluidity, but also it helps maintain the structure of the membrane.
Bibliography: http://biologymad.com/cells/cellmembrane.htm http://www.bbc.co.uk/education/guides/zydsgk7/revision