Cell Theory

M.J. Schleiden, a German botanist in 1838 stated that "All plants are formed of one or more cells" . Theodre Schwann, a German Zoologist in 1839 stated that "All animals are fomed of cells, have nuclei and were enclosed by thin cell membrane instead of thick cell wall as found in plant cells " . Schwann described the cell as membrane bound, nucleus containing structure. They have published some basic properties of cells, which collectively appreciated as Cell Theory. 

Basic Postulates of Cell Theory:

The various points of cell theory are :

1.Each cell is made of a small mass of protoplasm having a nucleus and bounded by a cell membrane with or without cell wall. 

2. All cells are basically alike in structure & metabolism.

3.Organisms are composed of cells and their products. 

4. The functions of an organisms are due to activities and interactions of its cells .

Drawbacks of Cell Theory:

Important drawbacks to cell theory are given below :

1. Viruses are also cited as exception to the cell theory. In fact, they are not organisms and are not expected to be covered by the cell theory. They consist of a nucleic acid (DNA or RNA) core surrounded by a protein sheath .

2 . Bacteria and blue - green algae do not have an organized nucleus . Their genetic material (DNA) is not enclosed by a nuclear envelope and lies directly in the cytoplasm .

3. Certain fungi , such as Rhizopus, have hyphae composed of a multi - nucleated mass of cytoplasm without division into cells .

4.  Some tissues, e.g., connective tissues, have a good deal of nonliving material, the matrix, between the cells. There is no mention of intercellular material in the cell theory .