Statement A : Biologists cannot predict the number of prokaryote species.

Statement B : Many prokaryote species are not culturable under laboratory conditions.

Biologists are not sure about how many prokaryotic species there might be. The problem is that conventional taxonomic methods are not suitable for identifying microbial species and many species are simply not culturable under laboratory conditions. If we accept biochemical or molecular criteria for delineating species for this group, then their diversity alone might run into millions.