Which macromolecule forms a double layer as the primary structure of cell membranes?

Phospholipids form the lipid bilayer that are the basis of cell membranes. 

This is what i found on google“ the monomers combine with each other via covalent bonds to form larger molecules known as polymers. in doing so, monomers release water molecules as byproducts. this type of reaction is known as dehydration synthesis, which means “to put together while losing water. in the process, a water molecule is formed.” i hope this you