Cell theory refers to the idea that cells are the basic unit of structure in all living things. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Development of this theory during the Mid 1600s was made possible by advances in microscopy. Microscopy is the technical field of using microscopes to view samples or objects This theory is one of the foundations of biology. Foundations of modern biology There are five unifying principles 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.

Contents 1 History of cell theory 1.1 Classical Cell Theory 1.2 Modern cell theory 1.3 Exceptions to the theory 1.4 Types of cells 2 References 3 See also 4 External links

History of cell theory

The cell was first named by Robert Hooke in 1665. Cork cambium is a tissue found in many vascular plants as part of the Periderm. Robert Hooke, FRS (18 July 1635 – 3 March 1703 was an English Natural philosopher and Polymath who played an important role in the 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) . Cork cambium is a tissue found in many vascular plants as part of the Periderm. Hooke's description of these cells was published in Micrographia. Micrographia is a historical book by Robert Hooke, detailing the then twenty-eight year-old Hooke's observations through various lenses. ^[1]. The cell walls observed by Hooke gave no indication of the nucleus and other organelles found in most living cells. In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed 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". Antonie Philips van Leeuwenhoek (October 24 1632 &ndash August 30 1723 was a Dutch tradesman and Scientist from Delft, the Netherlands Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms Spirogyra is a Genus of filamentous green algae of the order Zygnematales, named for the helical or spiral arrangement (see). Leeuwenhoek probably also saw bacteria ^[2]. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Cell theory was in contrast to the vitalism theories that had been proposed before the discovery of cells. Vitalism, as defined by the Merriam-Webster dictionary is a doctrine that the functions of a living organism are due to a vital principle distinct from physicochemical

The idea that cells were separable into individual units was proposed by Ludolph Christian Treviranus^[3] and Johann Jacob Paul Moldenhawer^[4]. Ludolph Christian Treviranus ( September 18, 1779 - May 6, 1864) was a German Botanist who was born in Bremen. Johann Jacob Paul Moldenhawer ( 11 February 1766 - 21 August 1827) was a German Botanist who made a number of important 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]

The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow, and others led to the development of the cell theory. René Joachim Henri Dutrochet ( November 14 1776 - February 4 1847) was a French Physician, Botanist and 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. Not to be confused with army general Theodore Schwan. ---- Theodor Schwann ( December 7, 1810 &ndash January Matthias Jakob Schleiden ( April 5, 1804 - June 23, 1881) was a German Botanist and co-founder of the Cell theory Rudolf Ludwig Karl Virchow ( 13 October 1821 &ndash 5 September 1902) was a German doctor, anthropologist, public health 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.

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.

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. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called
2. All cells come from pre-existing cells by division.
3. Energy flow (metabolism and biochemistry) occurs within cells. In Ecology, energy flow ( calorific flow) refers to the flow of Energy through a Food chain. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as
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

Exceptions to the theory

1. Viruses are considered by some to be alive, yet they are not made up of cells. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable
2. The first cell did not originate from a pre-existing cell. See: Origin of life. In the Natural sciences, Abiogenesis, or origin of life, is the study of how Life on Earth emerged from Inanimate Organic

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. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Eukaryotes, on the other hand, have distinct nuclei and membrane-bound organelles (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles). In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle In general vacuole functions include Removing unwanted structural debris Isolating materials that might be harmful or a threat to the cell Containing In addition, they possess organized chromosomes which store genetic material.

References

See also

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

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. See also List of basic cell biology topics. Cell biology (also called cellular biology or formerly cytology, from the Cell division is a process by which a cell, called the parent cell divides into two or more cells called daughter cells. Cell signaling is part of a Complex system of Communication that governs basic cellular activities and coordinates cell actions Cellular adhesion is the binding of a cell to another cell or to a Surface or matrix. In Developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized Cell type. Tavassoli (1980)
• The Cell Theory, Past and Present by Wm. Turner (1890)

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