Which of the following is NOT a characteristic of ectotherms?

Ectotherms, commonly known as cold-blooded animals, rely significantly on external environmental conditions to regulate their body temperature. They are characterized by their metabolic rates, which are generally lower during extreme temperatures, allowing them to conserve energy when it is most needed, such as in very cold or hot conditions.

Option B describes active movement independent of ambient temperature, which is typically a characteristic of endotherms, or warm-blooded animals. Endotherms can maintain a stable internal temperature regardless of external conditions, allowing them to be active even when the environment is not conducive to such activities.

In contrast, ectotherms must rely on the ambient temperature to dictate their energy levels and movement. When the temperature is too low, ectotherms tend to be less active since their biological processes slow down, and they may rely on the warmth of their surroundings to engage in activities.

The other characteristics, such as the ability to enter torpor for energy conservation or relying on external heat sources, directly align with how ectotherms function, emphasizing their dependence on environmental factors for thermoregulation. Thus, the distinction in option B illustrates a fundamental difference in the physiological mechanisms between ectotherms and endotherms.