• Robert Hook discovered dead cell in the 1665.
• Anton Von Leeuwenhoek discovered first living cell in 1674.
• Robert Brown discovered nucleus in 1831.
• Purkinjee gave the term protoplasm.
• T.H.Huxley described protoplasm as “physical basis of life” in 1868.
• Rudolf Virchow stated “omnis cellula e cellula”
• The German botanist Malthias Jacob Schleiden (1838) and the British zoologist Theodore Schwann in 1839
gave the cell theory.
• Further formalized by the German researcher Rudolf Virchow in 1855. In its modern form, this theorem has
four basic parts :

  1. The cell is the basic structural and functional unit of life; all organisms are composed of cells.
  2. All cells are produced by the division of pre-existing cells.
  3. All basic chemical and physiological functions – for example, repair, growth, movement, immunity,
    communication and digestion are carried out inside the cells.
  4. The activities of cells depends on the activities of sub-cellular structures within the cell (these subcellular
    structures include organelles, the plasma membrane and if present the nucleus)
    Electron microscope was invented by Knoll and Ruska. Scanning electron microscopes are used to examine
    the external parts of various organisms. The transmission electron microscope is used to view the internal
    structure of a cell and its organelles.
    • Organisms consist of more than one cell are called multicellular organisms. An organism with billions of cells
    begins life as a single cell which is the fertilized egg(zygote).
    • The single-celled organisms are called unicellular organisms. A single celled organism performs all the necessary
    functions that multicellular organisms perform.
    • Types of shapes of cells in bacteria
    In bacteria shapes of cells are of 4 main types
    (i) Rod shaped i.e. Bacilllus( pl. Bacilli) e.g. Bacillus subtilis
    (ii) Spherical shaped i.e. Coccus( pl. Cocci) e.g. Streptococcus sp.
    (iii) Spiral shaped i.e. Spirillum e.g. Azospirilum
    (iv) Comma shaped i.e. Vibrio e.g. Vibrio cholerae
    Pleomorphism is the ability of few cells to change its shape during their life cycle. This property is seen in
    many bacteria, fungi and in some plant cells.
    The White Blood Corpuscle (WBC) is the only animal cell that can change its shape
    Types of shapes of cells in eukaryotes:
    (i) Squamous, cuboidal, columnar shaped cells are found in epithelium.
    (ii) Muscle cells or muscle fibres are elongated in shape.
    (iii) Neuron is thread like in shape with extentions.
    (iv) Red blood cells are flexible biconcave in shape.
    (v) Green alga like Spirogyra, Zygnema have cylindrical cells.
    (vi) Cells in fungi are mainly long, branched and filamentous in nature.