Cell theory facts Kids Encyclopedia Facts

Microscopic section through one year old ash tree (Fraxinus) wood, drawing made by Van Leeuwenhoek.

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 three 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 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.

Cell history

Cells were discovered by Robert Hooke (1635–1703). He used a compound microscope with two lenses to look at the structure of cork, and to look at leaves and some insects. He did this from about 1660, and reported it in his book Micrographica in 1665.

Many other naturalists and philosophers tried out the new instrument. The structure of plants was investigated by Nehemiah Grew (1641–1712) and Marcello Malpighi (1628–1694). Grew's major work was The anatomy of plants (1682). It is not clear who first saw animal cells, Malpighi, Jan Swammerdam (1637–1680) or Antonie van Leeuwenhoek (1632–1723).^p17

Leeuwenhoek's discoveries and drawings of 'little animalules' opened up a whole new world for naturalists. Protozoa, and microorganisms generally were discovered. Christian Gottfried Ehrenberg's book Die Infusionsthierchen summarised what was known in 1838. Lorenz Oken (1779–1851) in 1805 wrote that infusoria (microscopic forms) were the basis of all life.

The work of the Czech Jan Purkyně (1787–1869) and his student and collaborator Gabriel Valentin (1810–1883) was "unjustly denigrated by the nationalistic Germans. They have a claim to some priority in the cell theory".^{Chapter 9}

Johannes Müller (1801–1858) also made great contributions. It was, however, his student Theodor Schwann and Matthias Schleiden (1804–1881) who got the credit for the cell theory, despite the fact that some of their observations were not correct, and their credits to previous workers were "a travesty".^p97 As understood now, the cell theory includes these important ideas:

1. All living things are made of cells.
2. The cell is the basic unit of structure and function in all organisms.
3. Every cell comes from another cell that lived before it.
4. The nucleus is the core element of the cell.

The key works of Schwann and Schleiden were published in 1838 and 1839. These ideas still are the basic ideas of cell theory.

Images

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  Anton van Leeuwenhoek's microscope from the 17th century with a magnification of 270x.

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  Robert Hooke's microscope

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

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  Matthias Jakob Schleiden (1804–1881)
  

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  Theodor Schwann (1810–1882)