Which statement is true about fixatives based on the material?

• A. Glutaraldehyde is commonly used for electron microscopy
• B. Glyoxal fixatives are slower than formaldehyde
• C. Zinc cannot replace mercury in any fixative
• D. Bouin Solution is used for electron microscopy

Answer: (A)

Preserving ultrastructure is the main goal for electron microscopy, and the fixative chosen must create very stable cross-links to keep membranes and fine organellar details intact. Glutaraldehyde is a dialdehyde that cross-links proteins extensively, forming a robust protein network. This strong cross-linking locks in membranes and intracellular structures so they don’t collapse or distort during processing, which is exactly what EM needs for high-resolution imaging. That’s why glutaraldehyde is the standard primary fixative for electron microscopy, typically used in buffered solution and often followed by osmium tetroxide postfixation to fix lipids and boost contrast.

Bouin solution, while great for certain light-microscopy preparations, contains picric acid and is not suitable for EM because it can cause lipid extraction and other artifacts that degrade ultrastructural detail. Zinc-based fixatives do exist and can replace mercury-containing fixatives in some protocols, so the statement that zinc cannot replace mercury isn’t correct. Glyoxal fixatives are not the go-to choice for EM and don’t provide the same level of ultrastructural preservation as glutaraldehyde in standard EM workflows.