Answer:
Phospholipids form a bilayer in water because lipid consists of hydrophillic and hydrophobic regions.
Step-by-step explanation:
Lipid is known as amphipathic molecule because lipids has hydrophillic head and hydrophobic tail regions. The lipid molecules can rearrange themselves when they are dissolved in water.
Lipids when dissolve in water, the hydrophillic (water- loving) head interact with water whereas hydrophobic( water- hating) moves away from the water. This, makes the bilayer in water.