QS Study

Reproduction is one of the most important characteristics of organisms. The biological process by which an organism, to check its extinction, either singly or with the help of the opposite sex of the same species, produces progeny is called reproduction. Amoeba mainly produces its progeny by the asexual process. Asexual reproduction process is of two types, Binary fission and Sporulation.

1. Binary fission: Growth of the body is an important characteristic of organisms. With the suitable environment and proper food, the ‘amount of cytoplasm of the body of Amoeba increases also with the volume of the body. The growth of the body reaches to such an extent that its cytoplasm cannot perform the metabolic activities smoothly. At this stage, Amoeba starts to multiply by binary fission. In this process, one mother Amoeba divides into two daughter Amoebas.

The process is described below: At the beginning of the division, Amoeba withdraws its pseudopodia. The body then takes a circular shape. Its nuclear membrane disappears and the nucleus becomes larger and conspicuous. Gradually the nucleus takes a long shape and the mid-section contracts. At this time the endoplasm around nucleus becomes slightly loose. The chromosomes situated in the nucleus divide longitudinally. The two daughter chromosomes move towards the two opposite poles and the midsection becomes narrow. As a result, the nucleus takes the shape of a dumbell.

The cytoplasm then deposits surrounding the nucleus. About the same time plasmalema being folded enters towards the interior. Next, the nucleus is divided into two parts and the plasmalema folds meet together. As a result, the mother Amoeba transforms into two daughter Amoeba. In the meantime, the cytoplasm surrounding the nucleus which is being divided approaches the fold. At this stage, the nucleus is divided into two parts to form two daughter nuclei. Finally, the cytoplasm surrounds each nucleus. Next, the plasmalema is formed outside the cytoplasm. As a result, the mother Amoeba becomes transformed into two new small Amoebas. Then these new daughter Amoebas begin their own free life. To survive under unfavourable environment Amoeba produces a thick wall around its body. This is called cyst wall. This stage is known as the cystic stage.


2. Sporulation: Surrounded by a cyst wall in unfavourable condition, the nucleus of Amoeba is divided into multiple divisions and forms numerous spores. This process is known as sporulation.

In this process first nuclear membrane of Amoeba disappears and the nucleuos is divided into several chromatin segments by repeated divisions. They remain in free state inside the endoplasm. These chromatin parts then become encloses by the nuclear membrane. Later on cytoplasm surrounds these small parts and finally, plasmalemma is formed around them. Next, the spore membrane is formed outside the plasmalema. In this way in the body of an Amoeba more than hundred spores may be formed. Breaking the plasmalema, next these spores come outside. In a favorable condition, daughter Amoeba comes out from the spores.


Fig: Sporulation

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