Cell-Basic unit of life:Brief history about the discovery of cells
The study of cell is not possible without microscope. Anton van Leewenhoek (1632-1723) studied the structure of protozoa spermatozoa, bacteria, and red blood cells under the simple microscope that he observed under a compound microscope that was designed by him. The term cell was initially coined by Robert Hooke in the year1665 to designate the bare honey-comb like structures viewed in a thin part of bottle cork that he observed.
In the year1838, the German botanist Schleiden stated that all plants are build up of plant cells. After that, in 1839 his colleague, the anatomist Theodore Schwann studied and concluded that all animals are also comprised of cells. Even at that time the actual nature of a cell was a big question. The cell theory was again rephrased by Rudolf Virchow in the year1858.
In 1831, Robert Brown discovered the existence of nucleus in the cells of orchid roots. This was a significant discovery. Purkinje coined the word protoplasm for the slimy substance which is found within the cells. In the twentieth century, different modern micro methods have been utilized in cytological investigation. With the invention of electron microscope in 1932 more and more information regarding the cell and different organelles of the cells become available to us. On the basis of structure, the cells are categorized into prokaryotic and eukaryotic cells.
Eukaryotic cells differ very much in size and shape. Smallest cells are found among bacteria (0.2 to 50 microns). The biggest plant cell is the ovule of Cycas. The shape of the cells too varies considerably. It might be polygonal, spherical, oval, rectangular, cylindrical, ellipsoidal and so on.
Figure: Diagrammatic symbolization of eucaryotic Plant Cell
Figure: Diagrammatic symbolization of eucaryotic Animal Cell
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