The degree of saturation of phospholipids in a membrane will affect which of the following functions of phospholipids?

the ability of phospholipids to form phosphodiester bonds with other phospholipids
the formation of liposomes
the permeability of the membrane
the ability of the phosphate group to bind to a small-molecular-weight, hydrophilic molecule

The fluidity and the permeability of cell membrane must be maintained within a certain range for the cell to function properly.
The permeability of cell membrane depends on a number of factors, among them is the degree of saturation of fatty acids tails making up phospholipids.
Phospholipid tails can be saturated or unsaturated. Saturated tails have no double bonds and as a result have straight, unkinked tails, while unsaturated tails have double bonds and, as a result, have crooked, kinked tails.
Interactions between tails are maximized in the case of saturated tails, thus decreasing membrane fluidity and permeability, while unsaturated tails increases membrane fluidity.