Final answer:
Phospholipids are amphipathic molecules that form a bilayer in a cell membrane.
Step-by-step explanation:
A phospholipid is an amphipathic molecule, meaning it has a hydrophilic and a hydrophobic part. The "head" is composed of the hydrophilic phosphate group, and the “tail” contains the hydrophobic fatty acids. In a membrane, a bilayer of phospholipids is formed, with the hydrophilic heads facing the aqueous environment both inside and outside the cell, while the hydrophobic tails face each other. This structure allows phospholipids to form a two-layer cell membrane.