Cell

• Robert Hook found cells, by looking at a thin piece of cork. He said that cells look like tiny boxes or honeycombs he called it cellula [now cell].
• Whichever did Robert Hook discover Cell?

  1665
• Anton Van Leeuwenhoek Use a handmade microscope to look at a pond scum and discovered single cell organisms. he called them 'ANIMALCULES'. He also looked at blood cells from fish, birds, frogs and humans. He concluded that cells were in plants and animals too.
• Matthias Schleiden studied plant tissues under the microscope and concluded that all parts of a plant are made up of cells. He was the first person who stated that ALL LIVING THINGS ARE MADE UP OF CELLS.
• Matthew Schindler found that all plants parts are made of cells. He was a botanist.
• When did Matthew Sheldon discover cells?

  1838
• When did Anton Van Leeuwenhoek Discover animalcule?

  1673
• Theodor Schwann found that all animals are composed of cells. He was a zoologist.
• When did Theodor Schwann discover animal cells?

  1839
• Rudolph Virchow concluded that cells must arrive from a pre-existing cell. His theory stated, "Omni Cellula e Cellula" meaning all cells arrive from a pre-existing cell.
• When did Rudolph Vichrow derive his theory?

  1858
• Robert Brown discovered nucleus [Karyon] in 1831.
• Viruses are exceptions to the cell theory
• Animal cells-

  • The cell wall is absent in all animal cells. Cells are covered by a thin flexible living cell membrane.
  • Chloroplast and other plastids are generally absent.
  • The Golgi Complex is distinct, well-developed and lies near the nucleus.
  • Glycosomes are absent.
  • Nucleus is generally centrally located in the cytoplasm.
  • Few small sized food and contractile vacuoles may be present in cytoplasm.
  • They have centrioles and centrosomes.
  • Cytokinesis occurs by furrowing.
• Plant cells-

  • Cells are covered by thick, rigid cellulosic cell wall in addition to cell membrane.
  • Chloroplast and other plastids are present.
  • Golgi complex is indistinct in the form of unconnected units called Dictyosomes.
  • Glyoxysome may be present in seed cells.
  • the large sap vacuole pushes the nucleus to peripheral position.
  • Vacuoles are large and more in number. Large centrals are vacuole, food and contractile vacuole is absent.
  • Centrioles and Centrosomes are absent in plant cells but are present in lower plants.
  • Cytokinesis occurs by cell plating
• Smallest cells- Mycoplasmas [PPLO] (0.3 μm in length)
• PPLO- Pleuro Preumonia like organisms
• Long isolated single cell- Egg of an ostrich
• Longest cell- Nerve cell
• Size of bacteria- 3 to 5 μm
• Human RBC's- 7 μm in diameter
• Basic shapes of bacteria-

  • Bacillus [Rod like]
  • Coccus [Spherical]
  • Vibrio [Comma shaped]
  • Spirillum [Spiral]
• Gram staining


  Grouping of bacteria based on their reaction to Gram's stain
• Christian Gram developed the Gram staining technique


  1884
• Gram staining procedure


  1. Stain with Crystal Violet or Gentian Violet

  2. Treat with iodine solution

  3. Wash with water

  4. Wash with alcohol or acetone
• Gram negative bacteria


  Bacteria that do not retain the stain and become colorless after washing
• Gram negative bacteria

  • E. coli
• Gram positive bacteria


  Bacteria that retain the stain due to high lipid content of cell wall, which gets dissolved in organic solvents like acetone
• Gram negative bacteria are commonly stained with Safranin
• Gram positive-

  • They remain colored with gram strain even after washing with absolute alcohol or acetone.
  • The wall is single layered. Outer membrane is absent.
  • lipid content of wall is quite low.
  • Mesosomes are more prominent.
  • Fewer pathogenic bacteria belong to gram positive group
• Gram negative-

  • The which bacteria don't retain the stain when washed with absolute alcohol or acetone.
  • The wall is layered. Outer membrane is present.
  • Lipid content of wall is 20 to 30%.
  • Mesosomes are less prominent.
  • Most pathogenic bacteria are present in gram negative group.