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What do you mean by Amoeboid locomotion. Explain sol-gel theory with the help of diagram.

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Locomotion :

Amoeba locomotes with help of pseudopodia which is called as Amoeboid Locomotion. The pseudopodia are cytoplasmic processes which can form at any place on the surface. One to many pseudopodia form at a time but it locomotes in the direction of main pseudopodium. Some inorganic ions such as Ca++, Mg+ and K+ help in locomotion. Many theories have been put forth by different scientist to explain locomotion in Amoeba. Some of them are as follows :

  • Adhesion Theory : It is not found to be correct, hence discarded.
  • Rolling Movemen Theory : It was propounded by Jenning (1994). It is not found to be correct for Amoeba proteus. Hence, discarded.
  • Contraction Theory : It was propounded by Schultze (1875) but not found to be correct.
  • Surface Tension Theory : It was propounded by Berthold (1886). It is not found correct for Amoeba proteus.
  • Walking Movement Theory : It was propounded by Dellinger (1906). It is not accepted for Amoeba proteus.

  • Sol-Gel Theory : It was propounded by Hyman (1917). Later on, it as supported by Pantin (1923-26) and mast (1925) It is found to be correct. hence accepted universally.

  • The sol-gel theory involves following steps ;

(i) At the point of formation of pseudopodium, the plasma- gel converts into plasmasol and the plasmasol begins to flow. It is the beginning of pseudopodium formation.

(ii) The constant flow of plasmasol results in the growth of the pseudopodium. When the plasmasol strikes the hyalin cap, it converts into plasmagel which is called as gelation.

(iii) At the opposite end, the plasmagel converts into plasmasol to continue the supply of plasmasol. It is called as solation.

  • Molecular Folding and Unfolding Theory : It was propounded by Goldacre and Lorsch (1950) to explain sol-gel theory. The plasmagel consists of Unfolded protein molecules and the plasmasol has folded protein molecules (Microfilaments). The gelation involves unfolding of the microfilaments and solation involves folding of the microfilaments.

The folding & unfolding of the protein molecules take place at the cost of ATP.

  • Fountain Zone Contraction Theory : It was propounded by Allen (1962). According to it, the region near the tip of the forming pseudopodium the everting plasmosol changes into plasmagel to form a wall or fountain zone. As a result, the anterior region develops tension.

  • Hydraulic Pressure Theory : It was given by Rinaldi and Jahn (1963). According to it, at the posterior end the plasmagel contracts (Contractile protein fibres of Actin and Myosin) to create a hydraulic pressure on the plasmasol to flow anteriorly.

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