In a phospholipid, which part is hydrophilic?

• A. Phosphate head
• B. Fatty acid tails
• C. Glycerol
• D. Cholesterol

Answer: (A)

Hydrophilic regions are the water-loving parts that interact with the aqueous environment. In phospholipids, the polar head region includes a phosphate group attached to a glycerol backbone; this phosphate group is charged and polar, so it readily forms interactions with water. That makes the phosphate-containing head hydrophilic. The fatty acid tails are long nonpolar chains that avoid water (hydrophobic), which is why they face inward in a bilayer. The glycerol backbone helps connect head to tails but isn’t itself the primary hydrophilic feature, and cholesterol is largely hydrophobic with only a small polar hydroxyl group, not the hydrophilic head of a phospholipid.