Explain the structure and life cycle of Entamoeba histolytica with the help of neat and labelled diagrams.

Entamoeba histolytica is a monogenetic parasitic living in the large intestine of man and causes amoebic dysentery or amoebiasis.
Structure : Entamoeba histolytica passes through three stages in its life cycle namely:
1) Trophozoite : It is the feeding and pathogenic stage. It lives in wall of large intestine.It feeds on RBC. Presence of RBC in food vacuoles and cart wheel shaped nucleus are the characteristic features of the trophozoite.
2) Precystic stage :It is non-feeding, non-motile, non-pathogenic stage of Entamoeba found in the lumen of the large intestine. The cytoplasm contains glycogen granules and chromatoid bars.
3) Cystic stage : It is round in shape. It is surrounded by a cyst wall. It is found in the lumen of intestine. Process of development of cyst wall is called encystation. It has four nuclei.
Life cycle shows three stages.
i) Trophozoite stage ii) Precystic stage iii) Cystic stage
* Trophozoite stages undergo binary fission in the wall of large intestine.
* Some of the daughters enter the lumen of the intestine, and transform into precystic stages.
* Precystic stage develops a cyst wall and transforms into cystic stage.
* Nucleus of cystic stage undergoes two mitotic divisions to form tetranucleate cysts. They are released out through faecal matter.
* They infect new host through contaminated food and water.
* In the small intestine of the new host cyst wall is digested.
* Metacystic stages are released. They undergo binary fission and develop into trophozoites.