Lipid bilayer

A lipid bilayer is a double layer of special fat molecules called phospholipids that forms the fundamental structure of cell membranes. Each phospholipid has a head that likes water (hydrophilic) and two tails that dislike water (hydrophobic). These molecules arrange themselves with the heads facing outward toward the watery environments inside and outside the cell, while the tails tuck inward, away from water. This creates a flexible, semi-permeable barrier that controls what enters and exits the cell, maintaining the internal environment vital for cellular function.