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Given a scientific passage and an answer, generate a question for the given answer.

Passage: Biochemical reactions are optimal at physiological temperatures. For example, most biochemical reactions work best at the normal body temperature of 98.6F (37C). Many enzymes lose function at lower and higher temperatures. At higher temperatures, an enzyme's shape deteriorates, and only when the temperature comes back to normal does the enzyme regain its shape and normal activity. Answer: enzymes
Output:
Biochemical reactions are optimal at physiological temperatures because many what lose function at lower and higher temperatures?