Immune system consists of many different cells, some of which acts as a part of innate immunity while lymphocytes are major players.
Phagocytosis is a process in which specialized cells engulf and digest extracellular pathogens. It is an important innate defense mechanism.
Innate Immunity is present right from the birth but acquired or adaptive immunity is acquired during the course of life.
Complement system is a part of the innate immune system