Cells also have cytoplasmic organelles and bubble-like vesicles that are made of membranes very similar to the cell membrane. These help to maintain several unique chemical enviroments within cells. The exact nature and composition of each of these aren't fixed and can vary considerably from membrane to membrane and also from time to time in the same membrane.
Phospholipids are O amphipathic .
Membrane phospholipids differ widely in the precise composition of their polar heads and their non-polar tails, but all have the same amphipathic property. The molecules in the two layers have opposite orientations, so that the non-polar, hydrophobic ends associate with each other and the polar, hydrophilic ends face the extracellular and intracellular aqueous environments. This simple, stable bilayer arrangement of phospholipids is the fundamental structure of cell membranes. Membrane proteins are embedded in the lipid bilayer . They are held in the membrane because they have hydrophobic regions that like the non-polar, hydrophobic internal region of the lipid bilayer.