ANIMAL CELL

ANIMAL CELL

Cytology is the branch of biology which deals with the structures of cell and its organelles and their functions. Cell is made of protoplasm which is surrounded by cell membrane and contains a nucleus. Cell is generally defined as “Cell is the structural and functional unit of living organisms” or “Cell is the unit of life”.

History

The study of cell was possible by the discovery of microscope by two scientists named Z. Janssen and H. Janssen in 1590. The word cell is associated with the name of Robert Hooke. In 1665 he observed under the microscope small spaces surrounded by the walls in a thin section of cork. This looked like honey comb. He called these spaces as cells (lat. Cell=Hollow space) which mean hollow space. In 1674 A. Van Leeuwenhoek (1632-1723) improved the lens system of this microscope by grinding and was the first to observe bacteria. He also observed various protozoan, sperms, erythrocytes (RBC) etc. in 1759 K. F. Wolf (1733-94) started that cells are found in living substances.

In 1805 Lorenz Oken (1779-1851) said that every organic being originated and is made of cells. In 1824 French scientist R. J. H. Detrochet observed that each plant and animal tissue is formed by different kinds of cells. In 1831 Robert Brown discovered the nucleus and showed that it is present in all Cells.

The famous German botanist M. J. Schleiden in 1838 stated that the body of a plant is made of microscopic cells and each cell is the unit of plant. Another German Zoologist T. S. Schwann observed in 1839 that animal body is also made of cells. Combining these two views Schwann and Schleiden (1838-39) formulated the famous Cell theory. According to this theory-

(i) All living organisms are made up of cells.

(ii) Every organism originated from a cell.

(iii) Each cell is an independent unit, yet they function together resulting in an organism.

(iv) Cells originated by a process of building in which the nucleus plays the part of creater

In 1839 J. E. Purkinje and in 1846 Hugo Von Mohl proposed the name Protoplasm for the living substance present in a cell. After this study of cell progressed with the help of better microscopes and use of chemical and physical techniques of investigation .In 1875 Van Beneden observed the centrioles, in 1879 W. Fleming reported the chromatin of the nucleus and used the term mitosis for cell division in 1882. He was the first to observe mitochondria but called them bioplast in 1894. In 1897 Altmann and C. Benda named these as mitochondria. In the nerve cells of barn owl Comillo Golgi first observed the Golgi apparatus in 1898. The term chromo some was coined by Waldeyer (1888). Wilson (1900) first described the structure of a typical cell. Then M. Knoll and E. Ruska (1932) invented the electron microscope which helped us to know in great detail about plasma membrane, mitochondria, endoplasmic reticulum, ribosome, lysosome, pinocyte etc.