1. 2.4.1 Draw and label a diagram to show the structure of membranes (1).

2. 2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of the cell membranes (3) Heads=phosphate=polar=HYDROPHILIC heads suited to the emnvironment Tails=lipds=non-polar=HYDROPHOBIC repel water creating a barrier between the inside of the cell and the outside. tails create a barrier to charged particles.

3. Individual lipids attract each other through their charges Diagram of phospholipid bilayer.

4. 2.4.3 List the functions of membrane proteins (1).

5. 2.4.4 Define diffusion and osmosis (1). http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter2/animat ion__how_osmosis_works.html

6.  Diffusion: passive movement of particles from a region of high concentration to a region of low concentration.  Osmosis is the passive movement of water molecules from a regions of lower solute concentration to a region of higher solute concentration

7.  Alternatively the statement can be in terms of pressure. Movement from a region of high pressure to a region of low pressure.  However, most biological diffusion takes place through membranes and involves sources, sinks and diffusion gradient.

8. Sink- source -definitions The region that supplies and maintains the high concentration of particles are called the source. The place where the substances is continually removed (or changed) is called the sink.

9. e.g. sink and source Source = blood oxygen. Sink= respiring cell