And because this actually contains full charges and this one doesn't, the end, though, is 1000 times more likely to actually pass across that cell membrane and dissolve in that hydrophobic core section than that tryptophan amino acid. So we see that indo, an uncharged molecule that is structurally similar to the tryptophan amino acid, crosses the membrane 1000 times more likely or more quickly than the tryptophan in its zvitarion form, which is the form that exists at the physiological PH of around seven. Now, so we can basically summarize the following result. We see that for a molecule to actually dissolve across that cell membrane, it must be able to interact in a stabilizing way with those tails, with the hydrocarbon tails of those phospholipid molecules. And so non polar molecules can dissolve across the membrane, but polar molecules cannot. Now, technically, that is not actually the entire story because we see water molecules are actually an exception to that rule.