Question

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

Answer 1

The amoeba has three stages in its life cycle, viz. the trophozoite stage, the precystic stage and the cystic stage.

A. The trophozoite amoeba:

This is the growing or feeding stage of the parasite having the following features:

1. The trophozoite is somewhat elongated (Fig. 18.4A); measuring 18 to 40 µm, but the shape is not fixed as the animal constantly changes its contour.

2. The cytoplasm is divisible into a clear translucent ectoplasm and a granular endo­plasm.

Encystation:

In some cases, the trophozoites are dis­charged into the lumen from the intestinal wall and are transformed into precystic forms, which produce cystic forms. This phenom­enon is known as encystation and leads to the production of a different strain

B. Precystic amoeba:

1. This is slightly ovoid with a short and blunt pseudopodium projecting from one side (Fig. 18.4B).

2. Size varies from 10 to 20 µm.

3. The motility ceases and ingested par­ticles are extruded.

C. Cystic amoeba:

1. The parasite becomes rounded and surrounds itself by a highly refractile cyst wall.

2. Size varies from 7 to 20 µm.

3. Contains one or more chromatid bod­ies with round ends.

4. The cyst is uninucleate at the begin­ning, but undergoes double fission so that four nuclei are produced. The quadrinucleate stage is considered as the mature cyst wall.

Hope this will help you.... ✌

Answer 2

structure : entamoeba histolytica passes three distinct stages in its life cycle they are

trophozoites stage

pre cystic stage

cystic stage

trophozoite stage : it is most active, motile feeding and pathogenic stage that lives in the mucosa and submucosa membranes of large intestine. it has following parts in its body.

plasma lemma: the body of the trophozoite is surrounded by plasmalemma.

cytoplasm: its ectoplasm is different into outer clear ,viscous ,non - granular ectoplasm and inner fluid like granule endoplasm

endoplasm: ribosomes food vacuoles and vascular vwheel shaped nucleus are present in endoplasm. contractile vacuole ,ribosome, endoplasmic reticulum, Golgi apparatus mitochondria are absent

lobopodium: its anterior end has single finger like blunt pseudopodium called lobopodium

presence of RBC in food vacuoles and cartwheel shaped nucleus are the characteristics features of trophozoites of entamoeba histolytica

it produces proteolytic enzyme called histolysin.it dissolves mucosa and submucosa of gut wall and release blood, tissue debris ingested by the trophozoite

pre cystic stage

it is the non feeding and non pathogenic stage of entamoeba histolytica that is found in lumen of large intestine

it is a small ,spherical or oval, non motile form

this cytoplasm of pre cystic stage stores glucagen granules and chromatoid bars made of riboonucleo protein which act as reserve food.

cystic stage

it is round in shape and is surrounded by a thin delicate and highly resistant cyst wall

it is found in lumen of the large intestine

the process of development of Cyst wall is called encystation which is main to tide over the favourable condition while passing to a new host. soon after encystation the nucleus under goes two successive mitotic division to form four daughter nuclei .

this type of cystic stage is called tetranucleate cyst or mature cyst which is infective stage to man.