The technique shown in the image depends on the formation of which chemical group?

• A. Staining of proteins
• B. Aldehydes
• C. Dehydration of tissues
• D. Crystallization of lipids

Answer: (B)

Formation of aldehyde groups is what enables this technique. In periodic acid–Schiff (PAS) staining, carbohydrates such as glycogen and mucosubstances are oxidized by periodic acid to generate reactive aldehyde groups. These aldehydes then react with the Schiff reagent to produce a magenta color, highlighting structures rich in carbohydrates like basement membranes and glycogen. This dependence on aldehyde formation is what sets PAS apart. Staining of proteins, dehydration steps, or crystallization of lipids are not driven by aldehyde chemistry in this context.