A prokaryote

Cell theory refers to the idea that cells are the basic unit of structure in all living things. 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. Prokaryotic bacteria cell structure Prokaryotes (IPA: //) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Microscopy is any technique for producing visible images of structures or details too small to otherwise be seen by the human eye, using a microscope or other magnification tool. ... For other uses, see Biology (disambiguation). ...

[edit] History of cell theory

Drawing of the structure of cork

The cell was first named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the non living cells from a cork (cork) . Hooke's description of these cells was published in Micrographia.^[1]. 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 Anton Van Leeuwenhoek, who in 1674 described the algae Spirogyra and named the moving organisms animalcules, meaning "little animals".(see). Leeuwenhoek probably also saw bacteria ^[2]. Cell theory was in contrast to the vitalism theories that had been proposed before the discovery of cells. Cork cambium is a tissue found in many vascular plants as part of the periderm. ... Robert Hooke, FRS (July 18, 1635 – March 3, 1703) was an English polymath who played an important role in the scientific revolution, through both experimental and theoretical work. ... Cork cambium is a tissue found in many vascular plants as part of the periderm. ... Hookes drawing of a flea Micrographia is a historical book by Robert Hooke, detailing the then twenty-eight year-old Hookes observations through various lenses. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is separately enclosed within its own lipid membrane. ... Anton van Leeuwenhoek Anton van Leeuwenhoek (October 24, 1632 - August 30, 1723, full name Thonius Philips van Leeuwenhoek (pronounced Layewenhook) was a Dutch tradesman and scientist from Delft, Netherlands. ... For the programming language, see algae (programming language). ... This article is about the type of algae. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Vitalism is the doctrine that vital forces are active in living organisms, so that life cannot be explained solely by mechanism. ...

The idea that cells were separable into individual units was proposed by Ludolph Christian Treviranus^[3] and Johann Jacob Paul Moldenhawer^[4]. 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"^[5] Johann Jacob Paul Moldenhawer (11 February 1766 - 21 August 1827) was a German botanist who made a number of important discoveries in plant anatomy. ... Henri Dutrochet René Joachim Henri Dutrochet (November 14th 1776, Poitou - February 4th 1847, Paris) was a French physician, botanist and physiologist. ...

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 cells are produced from other 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"^[6]. In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells thus completing the classical cell theory. Theodore Schwann Theodor Schwann (December 7, 1810 in Neuss, Prussia - January 11, 1882, in Cologne) was a German physiologist, histologist and cytologist. ... Die Entwickelung der Meduse (The Development of the Medusas), in Schleidens Das Meer Matthias Jakob Schleiden (April 5, 1804 - June 23, 1881) was a German botanist and co-founder of cell theory. ... Dr. R.L.K. Virchow Rudolf Ludwig Karl Virchow (October 13, 1821, Schivelbein (Pomerania) - September 5, 1902, Berlin) was a German doctor, anthropologist, public health activist, pathologist, prehistorian, biologist and politician. ...

[edit] Classical Cell Theory

1. All organisms are made up of one or more cells .
2. Cells are the fundamental and structural unit of life.
3. All cells come from pre-existing cells.

[edit] Modern cell theory

The generally accepted parts of modern cell theory include:

1. The cell is the fundamental unit of structure and function in living things.
2. All cells come from pre-existing cells by division.
3. Energy flow (metabolism and biochemistry) occurs within cells.
4. Cells contain hereditary information (DNA) which is passed from cell to cell during cell division
5. All cells are basically the same in chemical composition.
6. All known living things are made up of cells.
7. Some organisms are unicellular, made up of only one cell.
8. Others are multicellular, composed of countless number of cells.
9. The activity of an organism depends on the total activity of independent cells

Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... In ecology, energy flow (calorific flow) refers to the flow of energy through a food chain. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... Wöhler observes the synthesis of urea. ...

[edit] Exceptions to the theory

1. Viruses are considered by some to be alive, yet they are not made up of cells.
2. The first cell did not originate from a pre-existing cell. See: Origin of life.

This article is about biological infectious particles. ... For the definition, see Life. ...

[edit] Types of cells

Cells can be subdivided into the following subcategories: prokaryotes and eukaryotes. Prokaryotes lack a nucleus (though they do have circular DNA) and other membrane-bound organelles (though they do contain ribosomes). Eubacteria and Archeabacteria are two divisions of prokaryotes. 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. Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are microscopic, unicellular organisms. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (), or archaebacteria, are a major group of microorganisms. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... Lysosomes are organelles in eukaryotic cells that contain digestive enzymes to digest macromolecules. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... Vacuoles are large membrane-bound compartments within some eukaryotic cells where they serve a variety of different functions: capturing food materials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to the cell, maintaining fluid balance (called turgor) within the cell, exporting unwanted substances from the...

[edit] References

[edit] See also

• Cell biology
• Cell division
• Cell signaling
• Cell adhesion
• Cellular differentiation

Cell biology (also called cellular biology or formerly cytology, from the Greek kytos, container) is an academic discipline that studies cells. ... This does not adequately cite its references or sources. ... Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. ... Schematic of cell adhesion The study of cell adhesion is part of cell biology. ... In the center of the diagram are three of the early steps in the development of a mammal. ...

[edit] External links

• http://fig.cox.miami.edu/~cmallery/150/unity/cell.text.htm
• http://www.biology.arizona.edu/cell_bio/tutorials/cells/cells3.html
• http://www.edu.pe.ca/vrcs/2003/courses/9science/timeline.htm
• http://www2.bc.edu/~strother/GE_146/lectures/12.html
• http://www.cellsalive.com
• The cell theory: a foundation to the edifice of biology by M. Tavassoli (1980)
• The Cell Theory, Past and Present by Wm. Turner (1890)