Question

How do phospholipids arrange themselves into a bilayer?

Answer 1

In simple terminology, phospholipids in cell membranes consist of a 'hydrophilic head' and a hydrophobic tail. A hydrophobic tail is a long organic chain repelled by water while hydrophilic heads are attracted to water (and most polar solvents). In bilayers the hydrophilic heads point toward the extracellular fluids while the hydrophobic tails align such that they face each other. Thus hydrophilic heads of the second layer phospholipids turn to the intracellular fluid. This is how a bilayer forms.