Characteristics of Phospholipids in Membrane Fluidity

In biological membranes, lipids play a crucial role in maintaining the structure and fluidity necessary for cellular function. A particular class of lipids, known as phospholipids, contain specific chemical properties that contribute to their ability to form bilayers in aqueous environments. These bilayers are essential components of cell membranes.

A typical phospholipid consists of a hydrophilic (water-attracting) 'head' and two hydrophobic (water-repelling) 'tails'. This unique arrangement allows phospholipids to spontaneously assemble into a bilayer, with heads facing the external medium and tails tucked away from the water.

Which of the following best describes a characteristic of phospholipids that contributes to membrane fluidity?