What is the cell theory ? Who propounded it and when ?

The cell theory was proposed by two scientists- Schleiden (1838)and Schwann (1839). It says that all the plants and animals are composed of cells and the cell is the basic unit of life. The cell theory was further expanded by Virchow (1855) by suggesting that all cells arise from pre-existing cells.

Main points of the Cell Theory as proposed by Schlieden and Schwann are:

• The Cell is the smallest living unit of life.

• It is so small that it is not visible to the naked eye.

• The shape of the cell varies in different organisms and within an organism.

• Size of cells also differs.

• All living cells exhibit certain basic properties like respiration, growth, metabolism etc.

• All living organisms are made up of cells or their products.

• Cells originate from a pre-existing cell. A mother cell divides to produce daughter cells. Hence, cells exhibit cell division.