TNPSC VAO Science Study Material In Tamil PDF Download

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TNPSC VAO Science Study Material In Tamil PDF Download

The aim of biology is to explain the living world in terms of scientific principles. Aristotle, the great Greek philosopher and teacher, is known as the father of biology and the French naturalist, Jean Baptiste-de Lamarck, was the first to used the word  ‘biology’ in 1800. Biology today is subdivided into numerous branches based on the molecule, the cell, the organism and the population.

Multicellular animals are called Metazoa which have been divided into two branches: Parazoa and Eumetazoa.

In Parazoa, the body of animal is made up of loose cells, have poorly differentiated tissues and have no organ or digestive cavity. E.g sponges.

In Eumetazoa the cells are properly arranged into tissues and organs. It is further classified on the basis of (a) the number of germ layers present in the embryo; (b) the symmetry of the body of the organism; and (c) mode of origin of mouth. Those animals which have two germ layers in the embryo are called diploblastic animals and those having three germ layers are called triploblasticanimals.

Two types of animals have been recognised on the basis of origin of mouths: Protostomia (mouth arising from or near the blastopore of gastrula; gastrula is an embryonic stage) and Deuterostomia (mouth arising anteriorly at some distance from the blastopore).

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