1.4.2 Explain how models such as the fluid mosaic model of cell membranes are interpretations of data used to develop scientific explanations of the structure and properties of cell membranes.

 fact → implications of the model 

- phospholipids are polar with a hydrophobic tail and hydrophilic head → they have two different responses to water.

- when suspended in water phospholipids naturally form bilayers with hydrophobic tails inside and hydrophilic head outside → suggests the phospholipid bilayer structure.

- experiments on the total area of a monolayer film of phospholipids extracted from cells compared to the surface area of the cells showed that the film was twice as large as the cell surface area → further supports bilayer model.

- in electron microscope images of cell surfaces proteins can be seen sticking out → proteins not in continuos sheet on membrane surfaces but form a mosaic amongst the lipids. 

- when lectins ( any class of proteins) which only react with carbohydrates are added to a membrane they are found only on the outside → carbohydrates found only on outside of membrane.

- some water-soluble substances pass into and out of cells → suggests proteins in membranes act as channels for movement of substances in and out.

- ionic and polar molecules do not pass easily through membranes by lipid soluble substances do→ membranes are made mainly of lipid

the accepted model of the structure is the fluid mosaic structure because it explains all the facts above.