Which substances cannot diffuse through the lipid bilayer?

Which substances do you think will diffuse across the lipid bilayer most quickly? Most slowly?

• carbon dioxide ethanol glucose glycerol oxygen urea water

• Answer:

  So the criteria for diffusing across the membrane quickly is being small (to get through the holes) and being uncharged (charged will be repelled by the membrane), and non polar (because polar molecules will associated with water and they need to brake those associations to get through the membrane). Using those criteria we can say that O2, CO2 and H2O will be fast. H2O is an exception as it is polar however there are water pores inside the membrane. O2 and CO2 are fairly small and non polar/uncharged. Glucose, Urea and glycerol are all big so I would say the are slower.