Introduction and structure of Amoeba proteus

           Amoeba is the most popular protozoan . It is regarded as the lowest form of animal ,as its body resembles tinyblob of jelly , and yet it contains all the equipment required by the organism to perform all the vital functions of life such as movement, nutrition ,respiration ,excretion ,reproduction etc. 

          The interesting characteristic of this animal is that it has no shape or its shape is constantly changing.

          Amoeba was first described by Rosenhof in 1755. Full and comprehensive account of the  biology of Amoeba had been given by H.I. Hirschfield in 1962.

Classification of Amoeba proteus :-

Phylum -:Protozoa

Subphylum -: Sarcomastigophora

Superclass -: Sarcodina

Class -:Rhizopodea

Subclass -:Lobosia

Order  - : Amoebida

Genus -: Amoeba 

Species -: proteus

Habitat of amoeba proteus :-

                 It is commonly found in ponds, ditches, lakes, pools,springs, slow-running water streams. It occurs in abundance in those water which contain bacteria and organic  substances ( aquatic vegetation ,leaves and twigs). 

Structure :-

1.Size:-

Amoeba is a unicellular and microscopic microorganism. Amoeba measures about 250 to 600 microns in maximum diameter.

2.Shape:-

Amoeba is a shapeless microorganism .It appears as an irregular colourless and translucent mass of protoplasm.it change, its shape continuously by expanding and contracting finger like process called pseudopodia when it contracts pseudopodia. It becomes spherical in shape.

3.Plamalemma :-

The body of Amoeba is covered by a very thin delicate plasma membrane called plasmalemma.This membrane is selectively permeable .Water and some small salute molecule can pass freely through it in both directions but certain large molecules cannot pass.

4.Cytoplasm :-

There is a dense mass of cytoplasm containing several organelles inside the plasmalemma.Cytoplasm is differentiated into two fairly distinct zones, an outer ectoplasm and inner endoplasm.

1. Ectoplasm

Ectoplasm is thin ,clear and transparent .It is somewhat contractile and under tension. Ectoplasm lying immediately beneath the plasmalemma. It is clearly visible at the tip of a pseudopodium where it form a hyaline cap.

2. Endoplasm

It is completely surrounded by ectoplasm. It is fluid like granular and semi transparent. The endoplasm must also be under pressure of the ectoplasm,as the ectoplasm.

3. Endoplasmic organelles

These organelles are the nucleus, contractile vacuole, food vacuole and water globules etc.

3a.Nucleus :- 

Nucleus of Amoeba is a single large flattened , discoidal and slightly biconcave disk. It may be lying anywhere in the endoplasm. It is bounded by a thin nuclear membrane which is double and intercepted by pores. A lattice is also found below the inner nuclear membrane.It plays some part in maintaining the flattened form of the nucleus.

3b. Contractile vacuole :-

 Posterior end of ectoplasm contains a single ,clear rounded and pulsating contractile vacuole, filled with a watery fluid and enclosed by a single membrane .Surrounding this membrane is a region containing many tiny feeder vacuoles and mitochondria. It helps in the osmoregulatory and excretory activities of the animal.

3c. Food vacuoles :-

When Amoeba  engulfs food with a drop of water. A number of spherical space,small and large, containing water and food in various phases of of digestion ,occur in the endoplasm. These are the the food vacuoles .Digestion takes place inside these food vacuoles .They disappear with the egestion of non digestible food from the body.

4. Water globules :- 

Water globules are several ,small and spherical vacuoles filled with a colourless fluid.

5. Other organelles :-

The endoplasmic reticulum, besides forming a network of tubules, occur as vesicles.

The ribosomes occur on some of the endoplasmic vesicles as well as scattered in the endoplasm.

The Golgi bodies are present as several groups of sac like tubes.

The mitochondria are more or less oval and have tubular cristae

Bipyramidal or plate like crystals and stored food abound in the endoplasm.

The lysosomes are membrane bound spherical bodies, scattered in the endoplasm.

4.Pseudopodia:-

Pseudopodia means false feet.These are irregular, blunt processes of the cell body. These are of variable size and are capable of protruded or retracted ,often with considerable speed . These are formed as a result of liquefaction and following forward of the cytoplasm .As many pseudopodia are formed simultaneously. Amoeba proteus is a poly podia species.Its pseudopodia are large and broad with rounded tips They move by a pressure flow mechanism and assist the animal in locomotion and food ingestion.