5. Cell Structure And Organization - part 01 - Cell,Totipotency and modern cell theory

 


5. Cell Structure And Organization - part 01 - Cell,Totipotency and modern cell theory


Cell :

  • Cell is called a structural and functional unit of life of all living organisms capable of independent existence and can perform all functions of life.
  • Cells may be spherical, rectangular, flattened, polygonal, oval, triangular, conical, columnar, etc.
  • Cell size varies greatly in various plants and animals. Some of them are not visible to naked eye. Some are barely visible while some are macroscopic. 
  • The smallest cell size can be seen in mycoplasma (0.3 μm in length), bacterial cell size is 3 to 5 μm, while the largest size of cell is seen in Ostrich egg (nearly 15cms).
  • Longest cells are nerve cells.
  • Cell theory was proposed by Schwann and Schleiden. However, in this theory, there was no explanation about formation of new cells. 
  • It was Rudolf Virchow (1855) who explained for the first time that new cells are formed by cell division from pre existing cells (Omnis cellula-e- cellulla).
  • In later years, advanced research in cytology led to modification in cell theory, which is now known as Modern Cell Theory.

Totipotency : 

  • It is the capacity or the potential of living nucleated cell to differentiate and divide to form any other type of cell and thereby a complete new organism.
  • A cell is totipotent because it has the entire genetic information of the organism in its nucleus. 
  • Embryonic animal cells are totipotent and termed as stem cells. 
  • Stem cells have great medical applications including cure for diseases.

Know the scientists

  • A German botanist Matthias Schleiden (1838) examined number of plants and concluded that various tissues of plants are composed of different types cells. 
  • At that time, a British zoologist Theodore Schwann (1839) proposed that cells are bound by a thin membrane. 
  • He also explained about existence of cell wall as a unique character of plant cell. 
  • On the basis of his observation, he proposed that animals and plants are made up of cells and products of cells.
Postulates of modern cell theory,

  1. All living organisms are made up of cells.
  2. Living cells arise from pre-existing cells.
  3. A cell is the structural and functional unit of life.
  4. Total activities of cells are responsible for activity of an organism.
  5. Cells show transformation of energy.
  6. Cells contain nucleic acids; DNA and RNA in the nucleus and cytoplasm.


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