Formaldehyde is used in the technique in the image as a

• A. Reducer
• B. Fixative
• C. Oxidizer
• D. Dehydrating agent

Answer: (A)

Formaldehyde acts as a fixative because it preserves tissue structure by cross-linking proteins. It forms methylene bridges between amino groups and other reactive sites in proteins, effectively immobilizing cellular components and halting enzymatic activity. This stabilization maintains morphology so that tissue architecture can be accurately observed after sectioning and staining. It’s not used to reduce or oxidize tissues, nor to dehydrate them—dehydration is accomplished later in processing with alcohols and clearing agents to prepare the tissue for embedding.