The answer is “it is the gap between neurons” and “it ensures that information travels in one direction only.”
The answer is most likely the last option.
The answer may be, Replication, but I am unsure.
A hemopheliac is someone with a bleeding disorder resulting from any missing clotting factors in their blood. Vasoconstriction isn't generally the problem in hemophiliacs, nor is it the destruction of pathogens. If fibrin threads are not present to help form the platelet plug, then excessive bleeding occurs. Fibrin is one clotting factor that a hemophiliac may be missing which is then causing the disorder.