Although the concentration of membrane components in the aqueous phase is low (stable membrane components have low solubility in water), there is an exchange of molecules between the lipid and aqueous phases.
Skønt koncentrationen af membranbestanddele i de omgivende væskefaser er ringe (idet stabile membranbestanddele er tungtopløselige i vand), foregår der en udveksling af molekyler mellem lipid- og vandfasen.