Question

The purpose of a mordant in the Gram stain is to:

make gram-negative cells visible.
prevent the crystal violet from leaving the cells.
make the flagella visible.
make the bacterial cells larger.
remove the simple stain.

Answer 1

A mordant, such as Gram's iodine, is used in the Gram stain to trap the crystal violet dye in the thick peptidoglycan layer of Gram-positive bacteria's cell walls, preventing it from being washed out during the decolorization step.

Step-by-step explanation:

The purpose of a mordant in the Gram stain is to prevent the crystal violet from leaving the cells. During the Gram staining procedure, after the primary stain crystal violet is applied, a mordant in the form of Gram's iodine is added. This substance helps form a complex with the crystal violet dye, trapping it within the thick layers of peptidoglycan found in the cell walls of Gram-positive bacteria. When the decolorizing agent (e.g., ethanol or acetone/ethanol solution) is applied, it cannot easily remove the dye from these cells due to the mordant's action, consequently, Gram-positive cells retain the purple stain. In contrast, Gram-negative cells, which have thinner peptidoglycan layers and an outer membrane, allow the dye to escape during the decolorization step and are later stained pink by the secondary counterstain, safranin.

Answer 2

The purpose of a mordant in the Gram stain is to:

The answer is "prevent the crystal violet from leaving the cells."

Step-by-step explanation:

Staining techniques are widely used to visualize those components that are too difficult to see with the use of a light microscope. Staining involves 3 major steps/processes that include: Counter staining (using Safranin), De-colorization (using ethanol/acetone), and, Staining with crystal violet (a water soluble dye). During the staining procedure, the bacteria are bathed in alcohol, which causes the cell walls to shrink. The primary stain of the Gram's method is crystal violet.

A mordant is classically defined as an ion that binds a chemical dye and keeps it in place and it used for intensifying stains in cell or tissue preparations. Iodine mordant is used in Gram's Staining.

Gram staining is performed when the chemical dye crystal violet is mixed with the mordant iodine. Gram staining differentiates bacteria by the chemical and physical properties of their cell walls and it also distinguishes between Gram-positive and Gram-negative bacteria. Gram staining is based on the ability of bacteria cell wall to retaining the crystal violet dye during solvent treatment.

The purpose of a mordant in the Gram stain is to prevent the crystal violet from leaving the cells, in other words, increase the affinity of the primary stain.