Which statement best describes isopentane prechilled to -150°C?

• A. Best freezing method for muscle enzyme demonstration
• B. Used as a dehydrant
• C. Used as a clearing agent
• D. Used to embed tissue in resin

Answer: (A)

Isopentane prechilled to -150°C is used as a rapid freezing bath to prepare tissue for cryosectioning, especially when demonstrating muscle enzymes. The extreme cold and liquid state of the bath allow heat to be removed from the tissue very quickly, creating tiny ice crystals. This rapid solidification minimizes ice-crystal damage to cellular structure and helps preserve enzyme activity, which is crucial for accurate enzyme histochemistry in muscle. It’s not used as a dehydrant, clearing agent, or embedding medium—the other roles belong to solvents like ethanol or acetone for dehydration, xylene for clearing, and resins for embedding. So, its purpose here is to provide the fastest, most enzyme-friendly freezing method for muscle enzyme demonstrations.