Final answer:
Phospholipids have hydrophilic heads and hydrophobic tails. In water, they form bilayers with tails facing inward and heads facing outward, creating stable, energetically favorable structures that make up cell membranes.
Step-by-step explanation:
The formation of a phospholipid bilayer is driven by the molecular structure of phospholipids themselves. Each phospholipid molecule comprises a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. These heads are attracted to the water because of their polar nature, whereas the tails, being non-polar, seek to avoid water.
When placed in an aqueous environment, phospholipids automatically arrange themselves so that the hydrophobic tails face inward, away from water, and the hydrophilic heads face outward. This arrangement naturally forms a bilayer, with an inner and outer surface of hydrophilic heads surrounding a core region of hydrophobic tails.
Furthermore, the amphipathic nature of phospholipids contributes to the essential stability of this structure. The tails congregate, protected from water by the heads, resulting in a stable, energetically favorable configuration that forms the basis of cell membranes and other intracellular components. In essence, the bilayer structure is a result of the phospholipids seeking to satisfy their dual affinity, with heads interacting with water and tails avoiding it.
In summary, the unique alignment of phospholipid molecules in water, driven by their amphipathic characteristics, results in the formation of a bilayer that is fundamental to the structure and function of cellular membranes.