Home » Cell: The unit of life » CELL THEORY


Posted on

  • Cell theory was proposed by Schleiden and Schwann in 1855 to explain the concept of the cellular nature of living organism. But they did not explain how new cells are formed.
  • Rudolf Virchow in 1858 made a generalization “omnis cellula e cellula” i.e., all cells comes from pre-existing cells.

The three fundamental facts of the cell theory are as follows

  1. All living organisms (animals, plants and microbes) are made up of cells and cell products i.e., cell is the structural unit of life.
  2. All metabolic reactions in unicellular and multicellular organisms take place in cell i.e., cell is the functional unit of life.
  3. Cells originate only from pre-existing cells, i.e., no cell can originate spontaneously or de novo.

Exceptions to cell theory

  1. Viruses are acellular and do not have a cellular components. But possess genetic material and show multiplication.
  2. In some organisms, the body is not differentiated into cells through it may have numerous nuclei (coenocytes, e.g., Rhizopus).
  3. Protozoans and some thallophytes have a uninucleate body (e.g., Acetabularia) which cannot be divided into cells. They are acellular.
  4. Bacteria and cyanobacteria do not have nucleus and membrane bound organelles.
  5. RBCs and sieve tube cells are without nucleus.
  6. Protoplasm is replaced by non-living materials in the surface cells of skin and cork.

Significance of cell theory

Cell theory is one of the fundamental generalization of biology.