Briefly describe the cell theory.

Explanation

Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells. Schleiden, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. Schleiden and Schwann together formulated cell theory. But this theory did not explain as to how new cells were formed. .Rudolf virchow first explained that cells divided and new cells are formed from pre-existing cells. He modified the hypothesis of Schleiden and Schwann and give a definite shape to cell theory. Which states that,
1) all living organisms are composed of cells and products of cells
2) all cells arise from the pre-existing cells.