Cell theory was given by Schleiden and Schwann which stated –

a) Bodies of all the plants and animals are made up of cells.

b) The cells are structural and functional units of life.

But it failed to state the origin of life.

Few years later, Rudolf Virchow stated that cells divide to produce new cells. So the modern cell theory is –

a) all living organisms are composed of cells and products of cells.

b) all cells arise from pre-existing cells.