Amphipathic Nature Drives Bilayer Formation

Steps:

• Phospholipids have hydrophilic heads that attract water and hydrophobic tails that repel it, making them amphipathic.
• In water, hydrophobic tails cluster together to minimize contact with water, while heads interact with the aqueous environment.
• A single layer cannot satisfy both; tails would be exposed, so molecules rearrange into a bilayer with tails inward and heads outward on both sides.
• This spontaneous structure minimizes free energy, explaining immediate bilayer formation.

Why A is correct:

• All three properties (1: hydrophilic heads; 2: hydrophobic tails; 3: amphipathic overall) define the driving force for bilayer assembly per hydrophobic effect principles.

Why the others are wrong:

• B omits amphipathicity, which integrates heads and tails for bilayer stability.
• C excludes hydrophobic tails, essential for inward clustering.
• D ignores hydrophilic heads, needed to face water on both bilayer surfaces.

Final answer: A