The Cell
Cell: The cell is the smallest fundamental, structural and functional unit of living organisms Or cell is the basic unit of life
Discovery: The word Cell was first used by Robert Hooke in 1665. He observed a piece of cork under microscope and found many small chambers in it. He named each chamber as a Cell. Another scientist Robert Brown discovered rounded body in the cells of Orchids in 1831. This body named as nucleus.
Note on Cell theory:
Cell Theory: This theory was proposed by two German scientists . Schleiden 1838 , Schwann 1839 and Virchow.
It is a fundamental theory. The main points of this Theory are as follows.
1 All organisms are composed of one or more Cells.
2 The cell is the structural and functional unit of life , Schleiden and Schwann described the cell a denovo Structure. i.e it could arise from non-cellular material, but a German scientist Rudolf Virchow in 1855 added a Third very important point of the cell Theory .
3 A new cell is always produced only by the division of pre-existing cell. It is not a denovo Structure
Importance of Cell Theory: it brought a great revolution in the field of biology and proved that the body of living organisms performs all activities and functions by the interactions of Cell units.
Note on Microscope:
Microscopes are the instruments which are used to observe microorganisms or small organisms.
Kinds of Microscope:
There are different kinds of Microscopes. These kinds are as follows:
1) Light microscope
2) X-ray microscope
3) Electron microscope
1) Light microscope: in this microscope visible light is used as a source of illumination.
1) Simple microscope or Dissecting Microscope:
In this microscope single lens is used to study the object.
2) Compound Microscope:
In this microscope more than one lenses are used.
2) X-ray Microscope:
In this microscope short wave length X-ray are used as source of light. This microscope is very efficient instrument to observe the Three dimensional structure of cell parts.
3) Electron Microscope:
In this microscope Electron beam is used for illumination.
In this type of Microscope. Electron beam is emitted from the source (cathode or metal filament). This beam passes through the specimen and image is seen on a photographic film or on a screen.
