Cell Theory and Exceptions

The cell theory was given by three scientists, Matthias Schleiden, Theodor Schwann, and Rudolf Virchow in the 19th century. The cell theory states that:

- All living organisms are composed of one or more cells.
- The cell is the basic unit of structure and function in all organisms.
- All cells arise from pre-existing cells.

Exception to Cell Theory

The exception to the cell theory is the presence of viruses. Viruses are not considered living organisms because they cannot carry out the basic life processes on their own, such as metabolism and reproduction. They are composed of genetic material (either DNA or RNA) surrounded by a protein coat, but they lack the cellular machinery necessary for life.

Viruses can only replicate inside the living cells of other organisms, and they use the host cell's machinery to carry out their life processes. Therefore, viruses are not considered cells and are an exception to the cell theory.

In conclusion, the cell theory is a fundamental concept in biology, stating that all living organisms are composed of cells, and the cell is the basic unit of life. However, viruses are an exception to this theory because they lack the cellular machinery necessary for life and can only replicate inside the living cells of other organisms.

Schleiden and Schwann gave cell theory. R virchow made addition in 1855.
1- all organism are made up of cell.
2- cell is site of all metabolic activities
3- all cell arise from pre existing cell.
4- life of every organism start from single cell.
Virus is exemption from cell theory.