Have hydrophilic, polar (phosphate) head and a hydrophobic, non-polar (lipid) tail, make the membranes selectivelypermeable; arrange themselves so polar heads point out and the non-polar tails point in (form a micelle)
If there are enough they form a phospholipid bilayer, different membrane contain phospholipids with different fatty acids; affecting strength and flexibility
Hydrophobic/lipid soluble or tiny molecules pass through easily e.g. oxygen, carbon dioxide, and water (can’t pass through super easy - not hydrophobic)
Ions, hydrophilic molecules larger than water, and large molecules (e.g. proteins) do not move across the membrane on their own, they need to be transported across the bilayer
