Some surround vacuoles , others mitochondria , chloroplasts and the nucleus. Compartments are reaction areas clearly separated spatially. They consist mainly of lipids and proteins. They act as a permeability barriers and are permeable only for selected substances. When fragmented do they always reform as vesicles.
Phospholipids are the most common molecules in membranes.
This structure lends a tendency to form organized structures and monomolecular layers whose degree of organization is dependent on the length of the fatty acid residues and the number of double bonds to phospholipids. The hydrophobic parts of the molecule would point towards the inside of the double layer, the hydrophilic towards its outside. The lipids in the model form a double layer and the proteins are taken up by it. It explains the organization of the lipid molecules but could not account for numerous properties of membrane proteins without doubt. The model describes the membrane as a fluid mosaic.