Final answer:
The tails of phospholipids are composed of fatty acids and are hydrophobic in nature, forming the internal part of the cell membrane.
Step-by-step explanation:
The tails of the phospholipids of the plasma membrane are composed of fatty acids and are hydrophobic. Phospholipids are a major component of all cell membranes. Structurally, a phospholipid molecule has a glycerol backbone to which two fatty acids are attached, and a phosphate group that is linked to the glycerol. The fatty acid chains are hydrophobic, meaning they repel water, while the phosphate group is hydrophilic, meaning it attracts water. Consequently, when arranged in a bilayer to form the plasma membrane, the hydrophobic tails face inward, shielded from water, whereas the hydrophilic heads face outward towards the aqueous environment inside and outside of the cell.