The issue of unanswered question fraction is always in discussion (and it being a factor for site graduation).
In my opinion a lot of mechanisms are unknown in biology (even for some commonly observed processes). This is unlike the problems addressed in stackoverflow or any other discipline for which there will always exist a precise answer (or perhaps less number of unanswerable questions).
Have a look at these two questions:
- What are the side-effects of long-term liquid breathing?
- How does Sodium Valproate cause neural plasticity
There may be more like these. They are good questions, logically posed and clear. The issue is that we don't know the answers for these; the research community doesn't know the answers (I assume that because for these two questions I could not find any research papers that answer them).
What is/should be our policy on such currently unanswerable questions? They do increase our unanswered question count. It is justifiable to keep those questions until the answers are found out and someone posts them but I guess the purpose is to also give answers that are useful at present. One can always add new answers later.