Could you explain the structure of the plasma membrane to me? (A level)

The cell membrane, also known as plasma membrane, you will know from GCSE is a feature of both animal and plant cells that helps contain cellular contents and control entry and exit of substances from the cell. At A level, you will need to know that the plasma membrane is composed of a 'phospholipid bilayer'. Phospholipids are molecules that have a polar or hydrophilic (water-liking) phosphate 'head' and a hydrophobic (not water-liking) fatty acid 'tail'. Both the cytoplasm inside cells and the environment outside cells is aqueous (full of water). How can the hydrophobic fatty acid 'tails' of phospholipids avoid these aqueous environments? The answer is that phospholipids arrange themselves in a 2 layers (a bilayer) with the hydrophilic phosphate heads facing the extracellular environment/cytoplasm, whilst the fatty acid tails are shield from water in between. And so you have a phospholipid bilayer. It is also important to note that the plasma membrane is fluid - since individual phospholipid molecules can exchange places. Also, the phospholipid contains various proteins - like ion channels, facilitated diffusion transporters, as well as cholesterol that makes membranes stiffer.