Discovery of cell

 

Discovery of the Cell

Cells are the basic 'structural unit' of all living beings. They remained undiscovered for a long time because the majority of the cells are too small to be seen by the unaided eye.
  • Robert Hooke was the first scientist who observed thin slices of cork (obtained from the bark of a tree) through his self-designed microscope , in 1665.
  • He observed that they had honey-comb like structures consisting of little compartments (in Latin, 'cell' means 'a little room').
  • It was later explained that these 'compartments' were actually 'dead cells, bound by a 'cell wall'. 
  • The cells have the same basic structure, but they are different, with respect to their number, shape and size, in different living organisms.

Cell Number

  • An Amoeba and an earthworm are of different sizes. This difference, in the size of the organism, is due to the number of cells present in them.
  • While Amoeba is a living organism consisting of a single cell, an earthworm has millions of cells.
  • On the basis of their 'number of cells, living organisms can be classified into two categories
    (i) unicellular
    (ii) multicellular.


    Cell Shape

    • The shapes of cells differ not only in different organisms but also in different organs of the same organism.
    • They may be oval, spherical, cuboidal, fibre-like or polygonal.
    • These differences in shapes are due to their location and function in the tissue. For instance, a nerve cell has to transmit nerve impulses to organs located in different parts of the body. Hence, they possess a long fibre-like structure. 
    • The smallest cell PPLO (Pleuro pneumonia-like organism), also called mycoplasma, is about 0.1 micron (denoted as 'p') in diameter (1 p = 10-6m).
    • The ostrich egg, considered to be the largest cell, is (nearly) 170 mm in diameter. The hen's egg also represents a single cell; it is big enough to be seen with the unaided eye.

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