Ultrastructural preservation is obtained at physiologic pH within which range?

• A. 7.2–7.4
• B. 5.0–5.5
• C. 9.0–9.5
• D. 6.0–6.5

Answer: (A)

Ultrastructural preservation hinges on keeping the tissue environment at a pH very close to what it is in living organisms. At physiologic pH, about 7.35 to 7.45, proteins maintain their proper charges and structures, and fixatives can cross-link and immobilize cellular components without causing major pH-driven artifacts. Using a buffer in the neutral range, specifically around 7.2–7.4, helps stabilize membranes and organelles during fixation, yielding the best preservation for electron microscopy. More acidic conditions (roughly 5.0–5.5 or 6.0–6.5) can disrupt membranes and promote autolysis or extraction of components, while highly alkaline conditions (9.0–9.5) can also distort structures and staining. So, staying in the 7.2–7.4 range best maintains ultrastructural integrity.