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Gram staining identifies bacteria into gram positive and gram negative on the basis of:

Gram staining identifies bacteria into gram positive and gram negative on the basis of: Correct Answer Cell wall

Concept:

  • The scientist H.C. Gram differentiated the bacteria on the basis of staining
  • Gram Staining of bacteria is performed as below:
  1. Firstly, the bacteria are stained with Crystal Violet then with KI solution.
  2. After the staining, bacteria are washed with Acetone or Ethyl alcohol. 
  3. Due to washing, some bacteria lose their stain while the other retains them.
  4. Bacteria that retain stain (violet or purple) are called Gram + and bacteria that decolourise or lose the stain are called Gram - bacteria.
  5. Gram-negative bacteria are counterstained with Saffranine. 

Explanation:

  • Gram-positive bacteria have a thick cell wall made up of peptidoglycan. The crystal violet enters the cell and forms a complex with iodine.
  • This complex gives a purple stain to the cell wall.
  • Too large to pass through this thick wall, this crystal violet-iodine complex is not removed by the alcohol rinse (washing), and the stain remains violet.
  • Now, to counter the stain red-colored safranin dye is applied, but it gets masked by the crystal violet-iodine complex.
  • Gram-negative have a thin cell wall made of peptidoglycan, located between the cell membrane and the outer membrane.
  • The crystal violet-iodine complex can easily pass through this thin cell wall and hence it gets removed with the alcohol washing.
  • The counterstain safranin stains the cell pink or red.

Thus, it is clear gram staining identifies bacteria on the basis of the cell wall.​Additional Information

  • Cytoplasm: It is the jelly-like material present inside the cell, that is the main arena of all cellular activities.
  • Cytoplasmic granules: These are small condensed cellular materials that appear as spots. These are also called inclusion bodies. They perform the function of nutrient storage in bacteria 

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