Certified Endoscope Reprocessor (CER) Practice Test 2025 – Your All-in-One Guide to Exam Success!

Enzymes typically become ineffective at temperatures that exceed their optimal functioning range, which is usually around human body temperature (37°C or 98.6°F). As temperatures rise, the structure of enzymes can be altered due to denaturation, leading to a loss of their biological activity.

In this context, the choice of 140°F is aligned with the concept that many enzymes start to become denatured at higher temperatures, commonly around this range (approximately 60°C). At this elevated temperature, the enzyme's active site may change shape, preventing substrates from attaching effectively, thus rendering the enzyme inactive.

The other temperature options provided are below this critical threshold where enzymes maintain their functionality and may only begin to show slight inefficiencies. Therefore, 140°F is the point at which most enzymes begin to lose their effectiveness significantly, leading to a complete or near-complete loss of enzymatic activity.