INTRODUCTION

·        Just as a building is made up of bricks, the bodies of all plants and animals are made up of cells, i.e., all living beings show cellular organisation. Some organisms like Amoeba, Paramecium, bacteria, Chlamydomonas, etc. are made up of one cell (unicellular) only. There are a large number of other organisms like plants, animals, human beings etc.which are made up of millions of cells (multicellular).

·        Cell is the structural and functional unit of all living beings.

·        Robert Hooke (1665) discovered hollow cavities (empty boxes) like compartments in a very thin slice of cork (cell wall) with his crude microscope and named them as cellulae or cells.

·        Anton Von Leeuwenhoek first saw and described a live cell.

·        Robert Brown later discovered and named the nucleus in a cell. J. E. Purkinje, used the term protoplasm for the living substance present inside the cell.

·        The invention of the microscope and its improvement leading to the electron microscope revealed all the structural details of the cell.

·        Electron microscope : This was developed by Max Knoll and Ernst Ruska (1931) in Germany. It is a large sized instrument which has an internal vacuum, high voltage (50,000 – 1,00,000 volts), a cooling system, a fast beam of electrons (0.54 Å wavelength), a cathode filament of tungsten and electromagnetic lens (which has a coil of wire enclosed in soft iron casing) for focusing. It can magnify objects upto 2,00,000 times (now possible upto 2,50,000 – 4,00,000). The resolving power of electron microscope is 10 Å which is 100 times more than the light microscope. Study of living cells cannot be done through this microscope because of high voltage, which is required to operate it, as that can kill the living materials.

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