The cell theory

The three parts of cell theory were developed as a result of the work of not one, but many biologists and scientists over many decades. Robert Hooke was the first person to observe cells. He observed the dead cork cells under a simple microscope, and seeing the compartment like structure, he named the different “compartments” as cells. That originated the term “cell”.

This played a major role in scientific revolution, although Hooke had observed dead cells of cork. In 1674, Anton van Leeuwenhoek observed similar structures of cells in the living algae. This proved that living things were made up of cells. However it was not until Theodor Schwann and Matthias Schleiden in 1839 that the cell theory came into existence. They together worked out the two parts of the cell theory:

1.- All living things are made up of cells – that is, cell is the basic structural unit of life.

2.- Cell was the basic unit that performed life functions in an organism – that is, cell is the basic functional unit of life.

Rudolf Virchow, in 1858, concluded from his observations that all new cells come from preexisting cells, and this completed the three parts of cell theory:

3.- All new cells come from preexisting cells.

The credit of developing the three parts of cell theory is generally given to three scientists, Theodor Schwann, Matthias Schleiden and Rudolf Virchow.

Explanation of the three Parts of Cell Theory

  • Explanation of the first part of cell theory: Cell is the basic structural unit of life This statement implies that all living organisms, big or small, are made up of cells. Cell is the fundamental unit of all living organisms. Animals and plants, bacteria and fungi, algae and other such organisms, all are made of up either one or more (millions) of cells. If any organism is observed under a microscope, it is observed that it is made up of tiny block like structures which may have any shape. These are cells. Thus, we can say that sell is the basic structural unit of life. This is an image of a slice of cork cells as was seen by Robert Hook. It shows that the cork is composed of hundreds of cells packed together.


  • Explanation of the second part of cell theory : Cell is the basic functional unit of life The organisms are composed of one (in case of unicellular organisms), thousands (small organisms) or millions (big animals and plants) of cells. All these cells perform essential life processes that are vital to the running of life systems in the organism, which are vital for the existence of an organism. A cell performs all the necessary functions for life, for example, the process of production of energy from food takes place in cells of animals, the process of making of starch from CO2, water and sunlight is done inside all chlorophyll (a pigment) containing cells of plants, etc. Thus, all life processes of an organism are performed by individual cells, and due to the combined working of all the cells, a process or an action is performed. Thus it is clear that cell is the basic functional unit of life in a cell.


  • Explanation of the third part of cell theory : All new cells come from preexisting cells It is vital that new cells be produced continuously in an organism for growth, repair and replacement of old worn out cells. New cells are formed from old cells by cell division processes. A parent cell (old cell) divides into two new daughter cells (new cells) to keep up the process of growth of an organism, for repairing damages like wounds, injuries, and to replace the parent cell, which had become less efficient in doing its work than the daughter cells. Production of new cells is vital for the continuity of life processes of an organism. Rudolf Virchow discovered this part of the cell theory in 1858. This diagram represents the division of a parent cell into two new daughter cells.


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