<prompt> C5a act as aan?OpsoninChemotactic agentMACVasodilator  <response>: Ans. is b i.e., Chemotactic agent C5a is a powerful chemotactic agent. C3b, C3bi act as opsonin and enhance phagocytosis. C5-9 Called membrane attack complex MAC. It forms channel in the lipid membrane and causes cell lysis including bacteria. C5 is the point where both classical antibody dependent and alternative antibody independent pathways converge. Thus C5 forms the final common terminal pathway. 