Cell - Theory
Description:
Matthias Schleiden, a German botanist found that all plants have similar type of cells and all these cells have a cell wall.
Theodore Schwann a British Zoologist studies animal cells and observed that animal cells do not have cell wall. He observed that both plant and animal cells have more or less similar organization. He proposed the cell hypothesis which states that bodies of both animals and plants are formed of cells.
In 1839, Schleiden and Schwann combined their findings and formulated the cell theory. The postulated of the cell theory are as follows −
- All organisms are made up of cells.
- The cells contain hereditary materials and are responsible for the transfer of characters.
- New cells are formed de novo afresh from abiotic materials.
- Cells are responsible for all the metabolic activities inside the cells.
- A cell is a small mass of protoplasm usually containing a nucleus along with some other organelles.
Objections to Cell Theory
- Cell theory does not explain the formation of new cells.
- Cell theory suggested that new cells were formed inside old ones from the nucleus which was referred to as cytoblast.
Exceptions to cell theory
Viruses are made of nucleic acid and proteins so they do not have protoplasm like that of a cell.
Bacteria and blue-green algae which are prokaryotes lack well organized nucleus.
Coenocytic hyphae of fungus are multinucleate and aseptate. Such conditions are not explained in cell theory.