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

The correct answer is:

phospholipids

Phospholipids - they are made up of hydrophobic tails (inside the double layer) and hydrophilic heads (on the outside of the membrane).

Explanation:

Cell membranes comprise lipids (phospholipids and cholesterol), proteins and carbohydrates assemblies that are connected to some of the lipids and proteins. 

Phospholipids are composed of a polar head and non-polar (hydrophobic) tail. They line up such that the heads and the tail groups are side by side to form a single layer due to the information between the head groups and the tail groups. Two of these layers line up with the hydrophobic tail groups facing each other to prevent the hydrophobic groups away from the polar cover collections of other phospholipids and from the water in the adjoining environment.