Solution

The cell theory was jointly put forward by Schleiden and Schwann. It states that the bodies of all organisms are made up of cells and their products so that cells are units of both the structure and function of a living organisms. Four fundamental features of cell theory are:
(i) All living organisms are composed of cells and their products.
(ii) Each cell is made up of a small mass of protoplasm containing a nucleus inside and a plasma membrane with or without a cell wall outside.
(iii) New cells arise from pre-existing cells.
(iv) Activities of an organism are the sum total of activities and interactions of its constituent cells.