Archaea with cell walls consisting of a thick layer of complex polysaccharides often retain crystal violet dye when stained using the Gram-staining procedure. Suggest a reason for this staining reaction

This is because of the retention of the stain by the Gram positive bacteria.

Explanation:

Gram-positive bacteria are those that can retain the Gram stain. The cell wall of this bacteria is composed of a thick peptidoglycan layer which is rich in polysaccharides like N-acetyl glucosamine and N-acetyl muramic acid. These molecules are negatively charged and and they interact with the positively charged Gram's stain. Washing with acetone or ethanol is unable to remove of the stain due to the presence of mutiple layers of peptidoglycan that prevents the stain from escaping out thereby causing the bacteria to develop the characteristic violet colour of the stain. Gram-negative bacteria are those which cannot retain the Gram stain. Their cell wall has a very thin peptidoglycan layer. Hence, they are unable to trap the positively charged stain molecules when an acetone or ethanol wash is done. On washing most of the stain gets removed causing the bacteria to retain a pinkish colour.

The reaction of gram positive bacteria takes place in their peptidoglycan that is present in their cell wall which reacts with the stain and produce crystal violent color.

Explanation:

Archaea is a gram positive bacteria contain a thick cell wall which is made up of peptydoglycans.

This peptidoglycans react with the primary stain. When iodine is added, it binds with the crystal violet and thus trapped by the cells peptidoglycans.

Decoloration takes place by applying ethanol or acetone.

The dissociation of crystal violet gives rise to the formation of CV (Positive) and Chloride.

These ions then penetrate into the cell wall of the bacteria and then binding of CV (positive) ion with the negatively charged components in the bacteria and thus gives rise to the purple color stain.

Then iodine is added which reacts with positively charged Crystal violet and makes a complex called CV-I complex and this males the color of the cell purple.

Then decolorization stain called ethanol or acetone is added but the color does't change and takes up the counter stain called safranin but still the color becomes dark purple because of the dark purple color stain.