Final answer:
The investigation was carried out at 40°C because this is near the optimal temperature for enzyme activity in humans, which typically ranges from 37°C to 40°C, allowing enzymes to function most efficiently.
Step-by-step explanation:
The investigation was likely carried out at 40°C because this temperature is near the optimal temperature for enzyme activity, specifically for many of the enzymes present in the human body. Enzymes have a specific optimum temperature, at which they function most efficiently. Typically, this is close to 37°C to 40°C for human enzymes. At this temperature, enzymes are able to catalyze reactions at the maximum rate. Beyond the optimum temperature, enzyme activity tends to decline, and enzymes may become denatured at higher temperatures, losing their functional shape. In contrast, enzyme activity is reduced at lower temperatures and may be negligible near freezing point.