HISTORY AND DISCOVERY OF CELL AND EMERGENCE OF CELL THEORY

The cell can be defined as the structural and functional unit of life. It is the smallest unit that can carry out all activities of life. Cells are building blocks of complex multicellular organisms.

EMERGENCE AND IMPLICATION OF CELL THEORY: 

Study of cell (cell biology) began with the discovery of cell by Robert Hooke (1665), who reported his work in his famous publication “Micrographia”. He prepared and studied thin sections of cork (of dead plant material) under his self-made compound microscope. He observed that the cork is composed of minute honey comb like compartments which he termed as Cells. According to Hooke, cell is an empty space bounded by thick walls. Very little information was added to this idea in the following century. The work again started in the beginning of 19th century.

cell discovered by Robert Hooke

Lorenz Oken (1805) A German scientist believed that, “all living being originate from or consists of cells”.

Jean Baptist de-Lamarck (1809) expressed similar idea and said,"no body can have life if its constituent parts are not cellular tissue or are not formed by cellular tissue".

In 1831 Robert Brown reported the presence of nucleus in the cell. Due to this discovery Hooke's idea about the cell as an empty space was changed. It was later established that cell is not an empty space.

A German zoologist Theodor Schwann (1839) and a German botanist Schleiden (1838), working independently, came out with a theory called the Cell Theory.

They found that the cell consisted of 3 basic parts, viz nucleus, the fluid (cytoplasm) surrounding the nucleus, and an outer thin covering or membrane (plasma membrane). The cell wall, they said, was an additional structure, present only in plant cell. Keeping in view this definition of cell, the cells could be observed in plant as well as in animal according to cell theory; all living organisms are composed of cells and cell products.

The cell theory is one of the most fundamental generalizations in Biology. It has wide ranging effect in all fields of biological sciences. After the cell theory was presented, many details of cell were studied, as a result of which the cell theory was extended.

Rudolph Virchow (1855), a German physician, hypothesized that new cells were formed only by the division of previously existing living cells (to put it in Virchow's words: "omnis cellula e cellula"). It was contrary to the idea of "abiogenesis" (living things arise spontaneously from non-living things), one of the prevailing but controversial ideas about origin of life, at that time.

Louis Pasteur (1862), one of the greatest scientists of all times, supplied experimental proof for Virchow's hypothesis by demonstrating that micro-organisms (bacteria) could be formed only from existing bacteria. Original cell theory and Virchow's hypothesis gave us the basis for working definition of living things: living things are chemical organizations composed of cells and capable of reproducing themselves.

August Weismann (1880) said, “All presently living cells have a common origin because they have basic similarities in structure and molecules etc. It was shown that there are certain similarities in chemical composition, metabolic activities and structure, although they differ in many respects. Cells are basically similar but extraordinarily versatile. Cell is not only the structural but also the functional unit of living organisms. So cell theory is a very important unifying concept.

The salient features of Cell Theory in its present form are: 

• All organisms are composed of one or more cells.
•  All cells arise from pre-existing cells.
• Cell is the basic structural as well as functional unit for all organisms.