Lesson (1) Cell theory

Cell: The building unit of living organisms which can carry out all vital processes.

Cells have different shapes which are suitable for their functions, for example:-

Nerve cells (neurons):-

Neurons are long to be able to send messages from the spinal cord (in the vertebral column) to all body parts.

Fig. (1) Neuron

Muscle cells:-

They are long cells with cylinder shape which form muscle tissues. They have the ability to contract and relax to be able to move.

Fig. (2) Muscle cell

Scientists who took part in cell discovery:-

Robert Hooke

An English scientist who discovered cell. He invented a simple microscope in 1665 and examined a piece of cork using it. He concluded that it consists of a number of tiny vacuoles. He named these vacuoles "Cells"

à The word "Cell" is derived from the Latin word "Cellula" which means "Vacuole or small chamber"

Antoine Van Leeuwenhoek

A Dutch scientist who worked as an employee in the government. He was fascinated about lenses. In 1674, he used these lenses to make a simple microscope of magnification power 200x.

This microscope was used to examine blood, lakes water and other things. Therefore, Leeuwenhoek was the first to see the world of living cells and microorganisms.

Mathias Shleiden

A German scientist who discovered in 1838 that all plants consist of cells.

Theodor Schwann

A German scientist who discovered in 1839 that all animals consist of cells.

Rudolf Virchow

A German physician who stated in 1855 that:-

- Cell is not only the building unit of living organisms, but only the functional unit of them.

- Cells are produced only from cells that existed before them.

The efforts of those scientists formed the so-called " Cell theory" which is one of the most important theories in modern life science.

Cell theory has three laws, which are:-

1- All living organisms are composed of one or more cells. (See Shleiden and Schwann)

2- The cell is the basic unit of structure, function, and organization in all organisms. (See Rudolf Virchow)

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3- All cells come from pre-existing living cells (See Rudolf Virchow)

Light microscope

It was the only method available for scientists till 1950.

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