WJEC AS Biology - Cell membrane

Cell Membrane

The cell membrane is the boundary that separates living cells from their non-living surroundings. The cell membrane controls what substances pass into and out of the cell.

Structure of the membrane

The cell membrane is made up of proteins and phospholipids. 

The phospholipids have a phosphate head and two fatty acid tails.

The phosphate head is a polar molecule (hydrophilic which means water-loving) and has an attraction for other polar molecules such as water. 

The fatty acid tails are non-polar (hydrophobic which means water-hating) and repels water.

Phospholipids form a phospholipid bilayer with one sheet of phospholipid forming over another. The fatty acid tails face the inside of the bilayer so they can be as far away from the  water as possible, whereas the phosphate heads face the inside and outside of the cell so they can be nearer water.

Fluid Mosaic Model

In 1972 Singer and Nicholson put forward their theory of the fluid mosaic model. They proposed that:

•  There is a bimolecular phospholipid bilayer.
• Associated with the bilayer is a variety of protein…