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Cell theory

In 1838, Matthias Schleiden , a German botanist , examined a large number of plants and observed that all plants are composed of different kind of the cell which form the tissue of the plants . at about the same time Theodore Schwann (1839) , a British Zoologist ,studied different type of animal cell and reported that cells had a thin outer layer which is today known as the plasma membrane . He also conclude, based on his studies on plant tissue, that the presence of the cell wall is a unique character of the plants cells.

Schwann proposed the hypothesis that the bodies of animals and plants are composed of the cells and products of cells .

Schleiden & Schwann together formulated the cell theory . this theory however , did not explain as to how new cells were formed . Rudolf Virchow (1855) first  explained that cells cells divided and new cells are formed from pre-existing cells (Omnis cellula-e-cellula). He modified the hypothesis of Schleiden and Schwann  to give the cell theory final shape .

Cell theory as understood today is :-

(1) All living organisms are composed of cells and product of cells .

(2) All cells arise from pre-existing cells.

(3) Activities of an organism are the outcome of the sum total of the activities and interactions of its constituents cells.

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