Chemistry
How Lipid Bilayers Form Selectively Permeable Barriers Through Amphiphilic Self-Assembly
Quick fact
A single lipid bilayer is only about 5 nanometers thick—yet it's impermeable to ions like Na⁺ and K⁺, and to large polar molecules like glucose, while letting water and small nonpolar gases like O₂ and CO₂ pass through freely.
Why this is interesting
Your body is made of trillions of cells, and every single one is wrapped in a thin film that decides what goes in and out. But this film isn't a solid wall—it forms itself from tiny molecules that have a split personality. So how does a soap-like molecule build a barrier that's both sturdy and selectively open?