The development of the Fluid mosaic model

illustrates a lot about how scientists use imagination and evidence to develop models of the world.

Evidence for a phospholipid bi-layer

Data from the experiment which laid the foundations for a model of membrane

structure is summarised in the table below. Gorter and Grendel obtained the membranes of red blood cells. They calculated the area of the red blood cell membrane and then extracted the lipids that were present. These were dissolved in petroleum ether and allowed to spread into a layer one molecule thick on a surface of water and the area was measured.

From these results they concluded:

‘It is clear that all our results fit in well with the supposition that the erythrocytes (red blood cells) are covered by a layer of fatty substances that is two molecules thick.’

(From Gorter. E. and Grendel. F. Bimolecular layers of lipids on the chromocytes of the blood, 1924.)