Plasmodium completes its life cycle in two hosts, therefore, it is called digenetic endoparasite.Man is its primary host in which it completes its asexual cycle. Female Anopheles mosquito is its vector or secondary host in which it completes its sexual cycle.Sporozoites are present in the salivary glands of female Anopheles mosquito.They enter the human blood and reach the liver cells.In liver cells, the sporozoites undergo asexual multiple fission and form new cells called merozoites.Liver cells burst out to release the merozoites.These merozoites enter the RBCs and start the erythrocytic phase.Merozoites pass through trophozoite stage and signet ring trophozoite stage.Signet ring trophozoite ingests proteins of the cytoplasm of RBCs.It forms food vacuoles inside which it secretes digestive enzymes.These enzymes proteolysed blood haemoglobin and break it into protein globin and haematin pigment.Globin protein gets digested by the trophozoite.Unused haematin forms malarial pigment called haemozoin.Trophozoite increases in size and becomes rounded called schizont.Schizont undergoes multiple fission and forms many daughter nuclei.Haemozoin granules accumulate in the cytoplasm of RBCs.RBCs burst to release merozoites and the haemozoin granules.The release of haemozoin granules causes malarial fever.Merozoites lose the ability to reproduce and thus form gametes.These gametes enter the female Anopheles mosquito.Male and female gametes undergo fertilization to form immobile zygotes Later zygotes become worm-like and motile called ookinete which pierces peritrophic membrane and reach the outer layer of the stomach.The ookinete becomes rounded and encloses itself in a cyst and is called oocyst.Oocyst takes nutrients from the wall of the stomach and increases in size.Oocyst undergoes mitotic division and forms many micro daughter nuclei.In the cytoplasm, large irregular non-contractile vacuoles are formed.Daughter nuclei arrange around the surface of the vacuoles and get enclosed by cytoplasm.Inside oocyst, many lobes of cytoplasm are formed with the nucleus at its centre.Each lobe converts into the spindle-shaped structure and hangs down in the oocyst.Oocyst bursts and sporozoites become free in the haemocoel.Sporozoites swim in the haemolymph and reach salivary glands of the mosquito.