CELL- BASIC UNIT OR SUB UNIT OF LIFE

CELL- BASIC UNIT OR SUB UNIT OF LIFE

The word ‘cell’ is derived from the Latin word ‘Cellula’ which means a small compartment. The term was first coined by Robert Hooke (1635-1703) an English Microscopist. He observed a section of a bottle cork under a Microscope. Then he saw a honey comb – like structure consisting of a number of compartments. He published its illustration in a book called ‘Micrographia’, in 1665.
Cell is the most enigmatic mystery of nature about which it is believed that, the day scientists will understand it fully, they would be able to unravel the secret of life and death. With the advance of time, more advanced types of Microscopes became available which helped Robert Brown (1831) to find a conspicuous spherical body in each cell. He called it nucleus. By this time many scientists flung in this field. Mirabel (1819) advanced this statement by saying “Nobody can have life, if its constituent parts are not cellular tissue or are not formed by cells. “M.J.Schleiden and Theodor Schwann (1839) propounded the cell theory saying “The cells are organisms; and animals as well as plants are aggregates of these organisms arranged in accordance with definite laws”- and in 1855 Rudolf Virchow concluded that :Omnis Cellula-e-cellula, “i.e., new living cells arise only by reproduction of pre-existing living cells-i.e. the cell theory. Though credit for formulating this theory goes to him, it had already been postulated in pre historic Vedas.
The cells of all living organisms, though varying to a great extent in size, mass, shape, structure and function have many things in common. A cell has been variously defined, the cell is the structural and functional unit of plants and animals, or the cell is the unit of life or the cell is a mass of protoplasm surrounded by a thin membrane.
However there are many exceptions to cell theory. Eg, Vines and Venuses’ do not fit in the definition of a cell and these are therefore often described as living chemicals. These are supposed to be primitive organisms; which fail to reach a cellular state. Among other examples, coenocytes forms such as Rancheria (algae) and Rhizopus (fungus0 may also be found, placed outside the definition limit. These living substances are enclosed in a wall and there is hardly any organism like that of a cell. It is therefore difficult to accommodate these kinds of units in the context of cell theory.
A vast majority of cells range between 0.5 to 20 diameters. The biggest known cell is the egg of ostrich and the largest unicellular organism is Acetabularia. The fleshy cells of Citrus and Cucurbits are large enough to be seen by naked eyes. The shape of cell also varies depending upon their functions, needs of the organism and environmental conditions. A cell may be meristematic, Parenchy- matons, supporting, conducting, protective or reproductive in function. A typical plant cell has three distinct regions: (i) Cell wall, (ii) protoplasm and (iii) vacuoles. The protoplasm is living but cell wall and vacuoles are thought to be non-living though there is some difference of opinion about the non-living nature of cell wall.
The organism theory introduced by ‘Sharp’ (1934), rejects the idea of a plant or animal, being divided into separate physiological units. The metabolic activities of the whole plant are interrelated and the plant itself functions as a homogeneous entity. Hence, this theory emphasizes the importance of unity of protoplasm as a whole. It does not consider an organism as an aggregation of independent units. It considers the whole organism as the basic unit and the cells merely as its sub units.

Article By: Paulson K.J, St.Albert's College