Cell Theory 12:11 PM
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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 (Fig 1). Hooke's description of these cells was published in Micrographia. 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". Leeuwenhoek probably also saw bacteria. 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 and Johann Jacob Paul Moldenhawer. 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"
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 . 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". 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.

Modern Cell Theory

  1. The generally accepted parts of modern cell theory include:
  2. The cell is the fundamental unit of structure and function in living things.
  3. All cells come from pre-existing cells by division.
  4. Energy flow (metabolism and biochemistry) occurs within cells.
  5. Cells contain hereditary information (DNA) which is passed from cell to cell during cell division
  6. All cells are basically the same in chemical composition.
  7. All known living things are made up of cells.
  8. Some organisms are unicellular, made up of only one cell.
  9. Others are multicellular, composed of a number of cells.
  10. 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.

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