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, physiology, and organization in all living organisms.

History of Cell Theory

The cell was first named by Robert Hooke in 1665. He remarked that it looked strangely similar to "cells" or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the non-living cell walls from a cork. Hooke's description of these cells was published in Micrographia. [The American Naturalist, Vol.73 pgs 517-537] . The cell walls observed by Hooke 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". [ [http://www.euronet.nl/users/warnar/leeuwenhoek.html#references ANTONIE van LEEUWENHOEK] ] . Leeuwenhoek probably also saw bacteria [ [http://www.pubmedcentral.nih.gov/pagerender.fcgi?tool=pmcentrez&artid=413956&pageindex=1 Anton van Leeuwenhoek: tercentenary of his discovery of bacteria] by J. R. Porter in "Bacteriol. Rev." (1976) Volume 40, pages 260–269] . Cell theory was in contrast to the vitalism theories that had been proposed before the discovery of cells.

The idea that cells were separable into individual units was proposed by Ludolph Christian Treviranus [Treviranus, Ludolph Christian 1811, "Beyträge zur Pflanzenphysiologie"] and Johann Jacob Paul Moldenhawer [Moldenhawer, Johann Jacob Paul 1812, "Beyträge zur Anatomie der Pflanzen"] . All of this finally led to Henri Dutrochet formulating one of the fundamental tenets of modern cell theory by declaring that "The cell is the fundamental element of organization" [ [http://books.google.it/books?id=KwQOAAAAQAAJ&printsec=frontcover#PPA166,M1 Dutrochet, Henri 1924, "Recherches anatomiques et physiologiques sur la structure intime des animaux et des vegetaux, et sur leur motilite, par M.H. Dutrochet, avec deux planches"] ]

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 unit of structure and function in living things.

*All 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. By learning about cells and how they function, you can learn about all types of living things. 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 tenets of modern cell theory (see next section, below). 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" [Schleiden, Matthias Jakob 1839,"Contributions to Phytogenesis"] . In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells thus completing the classical cell theory.

Classical Cell Theory

#All organisms are made up of one or more cells.
#Cells are the fundamental functional and structural unit of life.
#All cells come from pre-existing cells.
#The cell is the unit of structure, physiology, and organization in living things.
#The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.
#Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).

Modern Cell Theory

The generally accepted parts of modern cell theory include:
# The cell is the fundamental unit of structure and function in living things.
# All cells come from pre-existing cells by division.
# Energy flow (metabolism and biochemistry) occurs within cells.
# Cells contain hereditary information (DNA) which is passed from cell to cell during cell division
# All cells are basically the same in chemical composition.
# All known living things are made up of cells.
# Some organisms are unicellular, i.e., made up of only one cell.
# Others are multicellular, composed of a number of cells.
# The activity of an organism depends on the total activity of independent cells.

Exceptions to the Theory

# Viruses are considered by some to be alive, yet they are not made up of cells.
# The first cell did not originate from a pre-existing cell.

Types of cells

Cells can be subdivided into the following subcategories:
#"Prokaryotes": Prokaryotes lack a nucleus (though they do have circular DNA) and other membrane-bound organelles (though they do contain ribosomes). Bacteria and Archaea are two divisions of prokaryotes.
#"Eukaryotes": Eukaryotes, on the other hand, have distinct nuclei and membrane-bound organelles (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles). In addition, they possess organized chromosomes which store genetic material.


ee also

*Cell biology
*Cell division
*Cell signaling
*Cell adhesion
*Cellular differentiation

External links

* [http://www.pubmedcentral.nih.gov/pagerender.fcgi?tool=pmcentrez&artid=1903404&pageindex=1 The cell theory: a foundation to the edifice of biology] by M. Tavassoli (1980)
* [http://www.pubmedcentral.nih.gov/pagerender.fcgi?tool=pmcentrez&artid=1328050&pageindex=1 The Cell Theory, Past and Present] by Wm. Turner (1890)

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Look at other dictionaries:

  • Cell theory — Cell Cell, n. [OF. celle, fr. L. cella; akin to celare to hide, and E. hell, helm, conceal. Cf. {Hall}.] 1. A very small and close apartment, as in a prison or in a monastery or convent; the hut of a hermit. [1913 Webster] The heroic confessor in …   The Collaborative International Dictionary of English

  • cell theory — n a theory in biology that includes one or both of the statements that the cell is the fundamental structural and functional unit of living matter and that the organism is composed of autonomous cells with its properties being the sum of those of …   Medical dictionary

  • cell theory — cell theory. См. клеточная теория. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Cell theory — Cellular Cel lu*lar (s[e^]l [u^]*l[ e]r; 135), a. [L. cellula a little cell: cf. F. cellulaire. See {Cellule}.] 1. Consisting of, or containing, cells; of or pertaining to a cell or cells. [1913 Webster] 2. porous; containing cavities. [PJC] 3.… …   The Collaborative International Dictionary of English

  • cell theory — noun (biology) the theory that cells form the fundamental structural and functional units of all living organisms; proposed in 1838 by Matthias Schleiden and by Theodor Schwann • Syn: ↑cell doctrine • Topics: ↑biology, ↑biological science •… …   Useful english dictionary

  • cell theory — ląstelinė teorija statusas T sritis augalininkystė apibrėžtis Biologijos teorija, pagal kurią visi organizmai yra sudaryti iš ląstelių. atitikmenys: angl. cell theory rus. клеточная теория …   Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

  • cell theory — cell′ the ory n. (lab cbl) bio the tenet in biology that cells are the basic units of structure and function in living organisms • Etymology: 1885–90 …   From formal English to slang

  • cell theory — noun Date: 1859 a theory in biology that includes one or both of the statements that the cell is the fundamental structural and functional unit of living matter and that the organism is composed of autonomous cells with its properties being the… …   New Collegiate Dictionary

  • cell theory — All organisms are composed of cell(s); a cell is the smallest unit of matter that is alive (functional unit) proposed by Schwann for animals in 1838 40; cells are the reproductive units of all organisms; cellular …   Dictionary of invertebrate zoology

  • cell theory — noun the theory that all living organisms are made of cells as the smallest functional unit …   Wiktionary

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