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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 that the cell is a fundamental unit of structure, function and organization in all living organisms.

Contents

History

Drawing of the structure of cork by Robert Hooke that appeared in Micrographia

The cell was first discovered by Robert Hooke in 1665. He examined (under a coarse, compound microscope) very thin slices of cork and saw a multitude 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. [1] Hooke's description of these cells (which were actually non-living cell walls) was published in Micrographia.[2]. 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".[3]. Leeuwenhoek probably also saw bacteria.[4] Cell theory was in contrast to the vitalism theories proposed before the discovery of cells.

The idea that cells were separable into individual units was proposed by Ludolph Christian Treviranus[5] and Johann Jacob Paul Moldenhawer[6]. 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"[7]

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 or organisms are made of cells.
  • New cells are created by old cells dividing into two.
  • Cells are the basic building unit of life.


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"[8]. In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells, thus completing the classical cell theory.

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Classical interpretation

  1. All organisms are made up of one or more cells.
  2. Cells are the basic unit of life.
  3. All cells arise from pre-existing cells.
  4. The cell is the unit of structure, physiology, and organization in living things.
  5. The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.

Modern interpretation

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 arise 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, i.e., made up of only one cell.
  8. Others are multicellular, composed of a number of cells.
  9. The activity of an organism depends on the total activity of independent cells.

Exceptions

  1. Viruses are considered alive by some, yet they are not made up of cells. Viruses have many features of life, but by definition of the cell theory, they are not alive. They are basically made up of proteins.
  2. The first cell did not originate from a pre-existing cell. There was no exact first cell since the definition of cell is imprecise.
  3. Mitochondria and chloroplasts have their own genetic material, and reproduce independently from the rest of the cell.

Types of cells

Cells can be subdivided into the following subcategories:

  1. 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 domains of prokaryotes.
  2. Eukaryotes: Eukaryotes, on the other hand, have distinct nuclei bound by a nuclear membrane and membrane-bound organelles (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles). In addition, they possess organized chromosomes which store genetic material.

See also

References

  1. ^ Inwood, Stephen (2003). The man who knew too much: the strange and inventive life of Robert Hooke, 1635-1703. London: Pan. pp. 72. ISBN 0-330-48829-5. 
  2. ^ Karling JS (1939). "Schleiden's Contribution to the Cell Theory". The American Naturalist 73: 517–37. doi:10.1086/280862. 
  3. ^ Moll WAW (2006). "Antonie van Leeuwenhoek". http://www.euronet.nl/users/warnar/leeuwenhoek.html#references. Retrieved 2008-11-25. 
  4. ^ Porter JR (June 1976). "Antony van Leeuwenhoek: tercentenary of his discovery of bacteria". Bacteriol Rev 40 (2): 260–9. PMID 786250. PMC 413956. http://mmbr.asm.org/cgi/pmidlookup?view=long&pmid=786250. 
  5. ^ Treviranus, Ludolph Christian 1811, "Beyträge zur Pflanzenphysiologie"
  6. ^ Moldenhawer, Johann Jacob Paul 1812, "Beyträge zur Anatomie der Pflanzen"
  7. ^ 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"
  8. ^ Schleiden, Matthias Jakob 1839,"Contributions to Phytogenesis"

Further reading

External links


]] 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 17th century 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 that the cell is a fundamental unit of structure, function and organization in all living organisms.

Contents

History

by Robert Hooke that appeared in Micrographia]]

The cell was first discovered by Robert Hooke in 1665. He examined (under a coarse, compound microscope) very thin slices of cork and saw a multitude 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.[1] Hooke's description of these cells (which were actually non-living cell walls) was published in Micrographia.[2]. 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 Antony van Leeuwenhoek, who in 1674 described the algae Spirogyra and named the moving organisms animalcules, meaning "little animals".[3]. Leeuwenhoek probably also saw bacteria.[4] Cell theory was in contrast to the vitalism theories proposed before the discovery of cells.

The idea that cells were separable into individual units was proposed by Ludolph Christian Treviranus[5] and Johann Jacob Paul Moldenhawer[6]. 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"[7]

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 or organisms are made of cells.
  • New cells are created by old cells dividing into two.
  • Cells are the basic building units of life.

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"[8]. In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells, thus completing the classical cell theory.

Classical interpretation

  1. All living organisms are made up of one or more cells.
  2. Cells are the basic unit of life.
  3. All cells arise from pre-existing cells.(omni cellulae e cellula)
  4. The cell is the unit of structure, physiology, and organization in living things.
  5. The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.

Modern interpretation

The generally accepted parts of modern cell theory include:

  1. The cell is the fundamental unit of structure and function in living organisms.
  2. All cells arise 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 in organisms of similar species.
  6. All known living things are made up of one or more cells.
  7. Some organisms are made up of only one cell and are known as unicellular organisms.
  8. Others are multicellular, composed of a number of cells.
  9. The activity of an organism depends on the total activity of independent cells.

Exceptions

  1. Viruses are considered alive by some, yet they are not made up of cells. Viruses have many features of life, but by definition of the cell theory, they are not alive.
  2. The first cell did not originate from a pre-existing cell. There was no exact first cell since the definition of cell is imprecise.
  3. Mitochondria and chloroplasts have their own genetic material, and reproduce independently from the rest of the cell.

Types of cells

Cells can be subdivided into the following subcategories:

  1. 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 domains of prokaryotes.
  2. Eukaryotes: Eukaryotes, on the other hand, have distinct nuclei bound by a nuclear membrane and membrane-bound organelles (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles). In addition, they possess organized chromosomes which store genetic material.

See also

References

  1. ^ Inwood, Stephen (2003). The man who knew too much: the strange and inventive life of Robert Hooke, 1635-1703. London: Pan. pp. 72. ISBN 0-330-48829-5. 
  2. ^ Karling JS (1939). [Expression error: Unexpected < operator "Schleiden's Contribution to the Cell Theory"]. The American Naturalist 73: 517–37. doi:10.1086/280862. 
  3. ^ Moll WAW (2006). "Antonie van Leeuwenhoek". Archived from the original on 2008-06-02. http://web.archive.org/web/20080602095555/http://www.euronet.nl/users/warnar/leeuwenhoek.html#references. Retrieved 2008-11-25. 
  4. ^ Porter JR (June 1976). "Antony van Leeuwenhoek: tercentenary of his discovery of bacteria". Bacteriol Rev 40 (2): 260–9. PMID 786250. PMC 413956. http://mmbr.asm.org/cgi/pmidlookup?view=long&pmid=786250. 
  5. ^ Treviranus, Ludolph Christian 1811, "Beyträge zur Pflanzenphysiologie"
  6. ^ Moldenhawer, Johann Jacob Paul 1812, "Beyträge zur Anatomie der Pflanzen"
  7. ^ 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"
  8. ^ Schleiden, Matthias Jakob 1839,"Contributions to Phytogenesis"

Further reading

External links


Simple English

Cell theory is a way to describe the biology of living things. Cell theory says that the cell is the basic unit of life. Cells by themselves are alive, but they can also be part of a larger living thing. The smallest living organisms (like bacteria but not viruses) and the biggest ones (like humans and whales) are all made of cells. Very small organisms like bacteria and amoebas are only made of one cell each, so they are called unicellular organisms ("uni" means "one"). Larger organisms are made of many cells, and they are called multicellular organisms.

Cell theory has 3 basic points:

  1. All living things are made of cells.
  2. The cell is the smallest living thing that can perform all the functions of life.
  3. All cells must come from pre-existing cells.

Cells are born from older cells, in a process called cell division. Cells contain information that is passed from the parent cell to the daughter cells, so that the daughter cells can do what they need to do. This information is carried on molecules called DNA.

Because cells are alive, they must be able to eat and do other things to stay alive. All cells have chemical ways of consuming food. These are part of its metabolism.

Even though there are many kinds of cells, they have some similarities too. Many of the chemicals inside of them are the same.

History

Robert Hooke discovered cells in 1663. He used a microscope to look at a piece of cork cambium. What he saw through the microscope reminded him of the small rooms that monks lived in. These rooms were called cellula in Latin, so Hooke called his discovery "cells". Hooke did not know that he was looking at dead cell walls and not living cells.[needs proof]. These cell walls did not have the nucleus and other organelles found in most living cells.

The first man to look at a live cell under a microscope was Anton van Leeuwenhoek. In 1674, he described the algae Spirogyra.[needs proof] He also described bacteria, which he called "animacules".[needs proof]


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