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Cell theory


Cell Theory refers to the idea that cells are the basic unit of structure in every living thing. Development of this theory during the Mid 1600s was made possible by advances in microscopy. This theory is one of the foundations of biology. The theory says that new cells are formed from other existing cells and the cell is a fundamental unit of structure, function and organization in all living organisms.
The cell was first discovered by Robert Hooke in 1665. He examined very thin slices of cork and saw billions of tiny pores that he remarked looked like the walled compartments of a honeycomb. Because of this association Hooke called them cells, the name they still bear. However, Hooke did not know their real structure or function. Hooke's description of these cells (which were actually non-living cell walls) was published in Micrographia.. His cell observations gave no indication of the nucleus and other organelles found in most living cells.

The first man to witness a live cell under a microscope was Antonie van Leeuwenhoek, who in 1674 described the algae Spirogyra and named the moving organisms animalcules, meaning "little animals". Leeuwenhoek probably also saw bacteria. Cell theory was in contrast to the vitalism theories that had been offered before the discovery of cells.

The idea that cells were separable into individual units was offered by Ludolph Christian Treviranus and Johann Jacob Paul Moldenhawer. All of this finally led to Henri Dutrochet formulating one of the fundamental rules of modern cell theory by declaring that "The cell is the fundamental element of organization".

The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow, and others led to the development of the cell theory. The cell theory is a widely accepted explanation of the relationship between cells and living things. The cell theory states:
•All living things are composed of cells.
•Cells are the basic units of structure and function in living things.
•Cells arise from pre-existing cells.

The cell theory holds true for all living things, no matter how big or small, or how simple or complex. Since according to research, cells are common to all living things, they can provide information about all life. And because all cells come from other cells, scientists can study cells to learn about growth, reproduction, and all other functions that living things perform.

Credit for developing Cell Theory is usually given to three scientists, Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow. In 1839 Schwann and Schleiden suggested that cells were the basic unit of life. Their theory accepted the first two rules of modern cell theory. However the cell theory of Schleiden differed from modern cell theory in that it proposed a method of spontaneous crystallization that he called "Free Cell Formation". In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells thus completing the classical cell theory.

Theodor Schwann (1810 – 1882) was a German zoologist. His many contributions to biology include the development of cell theory, the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast, and the invention of the term metabolism.
Once, when Schwann was dining with Matthias Jakob Schleiden in 1837, the conversation turned on the nuclei of plants and animal cells. Schwann remembered seeing similar structures in the cells of the notochord and immediately realized the importance of connecting the two phenomena. The similarity was confirmed without delay by both observers, and the results soon appeared in his famous Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals, in which he said that "All living things are composed of cells and cell products." Thus cell theory was definitely constituted. In the course of his verification of cell theory, in which Schwann traversed the whole field of histology, he proved the cellular origin and development of the most highly differentiated tissues including nails, feathers, and tooth enamel.
His generalization became the basic of modern histology, and in the hands of Rudolf Virchow (whose cellular pathology was an inevitable deduction from Schwann) placed modern pathology on a truly scientific basis.

Matthias Jakob Schleiden (1804 - 1881) was a German botanist and co-founder of the cell theory, along with Theodor Schwann and Rudolf Virchow.
Born in Hamburg, Schleiden was educated at Heidelberg and practiced law in Hamburg, but soon developed his hobby of botany into a full-time pursuit. Schleiden preferred to study plant structure under the microscope. While a professor of botany at the University of Jena, he wrote Contributions to Phytogenesis (1838), in which he stated that the different parts of the plant organism are composed of cells. Thus, Schleiden and Theodor Schwann became the first to develop what was then an informal trust as a principle of biology equal in importance to the atomic theory of chemistry. He also recognized the importance of the cell nucleus, discovered in 1831 by the Scottish botanist Robert Brown, and sensed its connection with cell division.
Schleiden was one of the first German biologists to accept Charles Darwin's theory of evolution. He became professor of botany at the University of Dorpat in 1863. He died in Frankfurt am Main on 23 June 1881.

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