Briefly describe the cell theory.
Ans. The Cell Theory was first proposed by Schleiden and Schwann in 1838-39. In their theory, they stated that (1) all living beings are products that are formed by one or more cells.(2) cells are the structural and functional units of life. A third statement was added to this theory by the works of Nagelli and Virchow. The cell theory was thus expanded to three statements –
(1) All living beings are products that are formed by one or more cells.
(2) Cells are the structural and functional units of life.
(3) new cells come from pre-existing cells.
In the modern cell theory, other points were also added. Some of them are-
(4) The basic composition is the same in all the cells.
(5) Energy flows occur in the cell.
Only viruses are an exception this Cell Theory as they are not made up of cells but of DNA and RNA materials.