Which statement correctly describes the amphipathic nature of phospholipids?

Which statement correctly describes the amphipathic nature of phospholipids?

• A. Phosphate head is hydrophilic, fatty acid tails are hydrophobic
• B. Fatty acid tails are hydrophilic, phosphate head is hydrophobic
• C. Both heads and tails are hydrophobic
• D. The entire molecule is hydrophilic

Answer: (A)

Amphipathic molecules have both water-loving and water-hating regions. In phospholipids, the phosphate-containing head is polar and interacts with water, making it hydrophilic. The two fatty acid tails are nonpolar hydrocarbon chains, so they avoid water and are hydrophobic. This arrangement drives bilayer formation in water: the hydrophilic heads face the watery surroundings, while the hydrophobic tails hide away from water in the interior. If the tails were hydrophilic or the whole molecule were hydrophilic, the bilayer structure wouldn’t form properly, and if both parts were hydrophobic, the molecule wouldn’t interact with the aqueous environment as needed for a membrane.

Amphipathic molecules have both water-loving and water-hating regions. In phospholipids, the phosphate-containing head is polar and interacts with water, making it hydrophilic. The two fatty acid tails are nonpolar hydrocarbon chains, so they avoid water and are hydrophobic. This arrangement drives bilayer formation in water: the hydrophilic heads face the watery surroundings, while the hydrophobic tails hide away from water in the interior. If the tails were hydrophilic or the whole molecule were hydrophilic, the bilayer structure wouldn’t form properly, and if both parts were hydrophobic, the molecule wouldn’t interact with the aqueous environment as needed for a membrane.