CAMLPR Histology Practice Test

The Periodic Acid Schiff stain targets carbohydrates, turning them magenta after oxidation to create aldehyde groups that react with Schiff reagent. This makes neutral glycogen, neutral mucins, basement membranes (which are rich in glycoproteins), and fungal cell walls readily visible. The best answer notes that PAS demonstrates glycogen, neutral carbohydrates including mucins, basement membranes, and fungi. For controls, liver (or cervix) is a reliable positive control for glycogen because these tissues contain abundant glycogen, while kidney provides a strong positive control for basement membranes due to the prominent glomerular basement membrane. Choices that assign staining to lipids or nucleic acids are not correct because PAS is specific for carbohydrates, whereas lipids are shown with lipid stains (like Sudan stains) and nucleic acids with other methods (such as Feulgen staining).