History and Origin 
A cell was defined as “unit of biological activity delimited by a semi permeable membrane and capable of self-reproduction
in a medium free of other living systems” by Loewy
and Siekevitz (1963).The study of cell has been made possible with the help
of light microscope. Robert Hooke (1665) with the help of light
microscope discovered that a section of cork is made up of small cavities surrounded by firm walls. He used the
term “cell” for the first time to describe his investigations
on the “texture of a piece of cork”. Later on A. Van Leeuwenhoek (1632-1723) observed various
unicellular organisms and cells like bacteria, protozoan’s, red blood
cells and sperm etc. He observed
nucleus in some erythrocytes and all
this was made possible with the improved microscopes. In 1809, Mirble M. stated
that all plant tissues are composed of cells. In the same year, importance of cells in living organisms
was described by J.B. Lamarck. Robert Brown
in 1831 observed nucleus in
certain plant cells. Mimosa cells
were boiled in nitric acid by Dutrochet (1837) to separate the cells
to conclude that all organic tissues
are composed of globular cells, united by simple adhesive forces. “All living organism are composed of cells” was stated
by Schwann, T. (1839) after
examining a variety of animals
and plant tissues.
On the basis of organization of membranes, variety and structure of cytoplasmic organelles and complexity of nuclear region, the cells are classified into two types: Prokaryotic cell and Eukaryotic cell. These terms were suggested by Hans Ris in 1960s.
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