When tissue is frozen slowly at -20°C, what artifact is commonly seen?

• A. No artifacts occur
• B. Large artifactual holes due to large ice crystals
• C. Rapid dehydration artifacts
• D. Improved morphology artifacts

Answer: (B)

Slow freezing allows water in the tissue to form large ice crystals. At -20°C, the cooling is relatively slow, so these crystals grow big enough to disrupt cell membranes and the surrounding matrix. When the frozen tissue is cut, those disrupted areas show up as large holes—artifacts from the ice crystals. Rapid freezing, by contrast, produces many tiny ice crystals that preserve structure better and reduce such holes. The other options don’t fit because no artifacts is incorrect, rapid dehydration artifacts relate to processing steps after freezing rather than the freezing itself, and “improved morphology artifacts” isn’t a recognized phenomenon.