Cell theory

Aristotal view about cell 

Aristotle presented organized observations to support the idea that all animals and plants are some how related
 Later this idea gave rise to questions like “is there a fundamental unit of structure shared by all organisms?”. But before microscopes were first used in 17th century, no one knew with certainty that living organisms do share a fundamental unit i.e. cell.

 Robert hook

  Cells were first described by a British scientist, Robert Hooke in 1665. He used his self- made light microscope to examines thin slice of cork. Hooke observed a “honeycomb” of tiny empty compartments. 
He called the compartments in the cork as “cellulae”. His term has come to us as cells . The first living cells were observed a few years later by the Dutch naturalist Antonie van Leeuwenhoek. He observed tiny organisms (from pond water) under his microscope and called them as “animalcules”. 

Jean Baptist de-Lamark 

 For another century and a half, the general importance of cells was not appreciated by biologists. In 1809, Jean Baptist de-Lamarck proposed that “no body can have life if its constituent parts are not cellular tissues or are not formed by c ellular tissues”.

 Robert brown

In 1831, a lush botanist Robert Brown discovered nucleus in the cell. In 1838, a German scientist Matthias Schleiden studied plant tissues and made the first statement of the theory. He stated that all plants “are aggregates of individual cells which are fully separate beings”. One year later, in 1839, a German zoologist reported that all animal tissues are also composed of individuas.

Schlieden and Schwann

Schlieden

Thus Schleiden and Schwann proposed cell theory in its initial 

 

Schewamm

form i.e. all living things are composed of living cells”. 

Rudolf Virchow  

Twenty years later in 1855 Rudolf Virchow, a German physician, proposed an important extension of cell theory. He proposed that all living cells arise from pre­existing cells . 

 Lious Pasture

 In 1862, Louis Pasteur provided the experimental proof of this idea. The cell theory is regarded as one of the most fundamental generalizations in biology. It has wide ranging effects in all fields of research. 
After the initial presentation of the cell theory by Schleiden and Schwann, many details of cells were studied and cell theory was extended. The cell theory, in its modern form, includes the following principles;  All organisms are composed of one or more cells, within which all life processes occur. Cells are the smallest living things, the basic unit of organization of all organisms. Cells arise only by divisions in previously existing cells. 

 Sub-cellular or Aceilular Particles: 

 According to the first principle of the cell theory all organisms are composed of one or more cells. Discovery of virus, prions and viroids claim that the statement is not so universal. They are not composed of cells; rather they are sub-cellular or aceilular particles, which do not run any metabolism inside them. 
But they show some characteristics of living organisms i.e. they can increase in number and can transmit their characters to the next generations.
 There are two general classes of cells: . The evolution of prokaryotic cells preceded that of eukaryotic cells by 2 billion years. 
 Streptococcus pyogenes, the bacterium that causes infections in the upper respiratory tract (e.g. sore throat), is an example of prokaryotes. Yeast, the organism that carries out fermentation and makes our bread rise, is an example of unicellular eukaryotes. Humans, of course, are an example of multicellular eukaryotes. We are well familiar with the basic organization of a eukaryotic cell. Here we will get some detailed learning about the cellular structure and functions.