Which classification describes an organism thriving at human body temperature (about 37°C)?

• A. Mesophile
• B. Psychrophile
• C. Thermophile
• D. Hyperthermophile

Answer: (A)

Organisms that thrive at human body temperature, about 37°C, are mesophiles. This temperature sits in the middle of microbial growth ranges, between the cold-loving and heat-loving groups. Mesophiles grow best at moderate temperatures, roughly 20–45°C, which includes the environment inside the human body. Psychrophiles prefer cold conditions and grow best below about 20°C, thermophiles prefer warmer conditions and grow best around 45–80°C, and hyperthermophiles thrive above 80°C. Since 37°C falls squarely within the mesophilic range, that classification is the best fit. This is also why many human-associated microbes are mesophiles—they’re adapted to the host’s normal body temperature.