The technique in the image depends on the presence of which substance?

• A. carbohydrates
• B. fats
• C. proteins
• D. nucleic acids

Answer: (A)

This staining method relies on carbohydrate-containing structures. Periodic acid oxidizes vicinal diols in sugars to form aldehyde groups, and the Schiff reagent then reacts with those aldehydes to produce a magenta color. Because the color development requires those aldehyde groups that come from carbohydrates (like glycogen, mucopolysaccharides, and basement membranes), the technique hinges on the presence of carbohydrates. Fats, proteins, and nucleic acids do not provide the same aldehyde-forming substrate in this reaction, so they do not give the characteristic color seen with this stain.