Here is your short paragraph on cell theory.
The plant body consists of a number of small, microscopic, box-like compartments called cells. In other words, the cells are the universal elementary units of organic structure.
A plant cell may be defined as microcosm having a definite boundary or the cell-wall within which complicated chemical reactions are going on. A cell devoid of this chemical reaction is inert and is considered to be a dead cell.
Schleiden (1838) and Schwann (1839) a German zoologist sponsored a theory that all animal and organisms are plant organisms are composed of cells. Schleiden (1838) and Schwann (1839) for the first time used the term Cell Theory and stated, “The cells are organisms, and animals as well as plants are aggregates of these organisms, arranged in accordance with definite law”. Schwann established the cell theory in a definite form. He had clear ideas both of morphological and physiological significance of the cell. According to him the cellular phenomena consists of two groups—(1) the plastic phenomena and (2) the metabolic phenomena.
The former one corresponds to morphology of cell and also includes in it “the combination of molecules which form the cell”. On the other hand the metabolic phenomena (physiologic phenomena) includes “the chemical changes, whether in the particles constituting the cell itself, or in the surrounding “cytoblastema”. Thus, about a century back Schwann expressed the present view point of cytology and, therefore, he is generally considered as ‘father of modern cytology’.
The cell theory postulates, in brief that the cells from the structural units of living organisms and the latter show a characteristic cellular construction. In addition, they are also functional units in that all the vital functions of the living organism are traceable ultimately to the living substance, the protoplasm contained in them.