Final answer:
Phospholipids have a hydrophobic tail and a hydrophilic head. They form a bilayer in the cell membrane, with the hydrophilic heads facing outward and the hydrophobic tails facing inward. This structure provides stability and selective permeability.
Step-by-step explanation:
A phospholipid is an amphipathic molecule, meaning it has a hydrophobic and a hydrophilic 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 and the hydrophobic tails facing inward, away from water. This arrangement provides structural stability while allowing selective permeability.