Final answer:
The statement is true. Endotherms can maintain a high activity level and metabolic rate regardless of external temperatures due to their internal heat generation, whereas ectotherms rely on external heat sources and are less active in cooler temperatures.
Step-by-step explanation:
The statement that endotherms can sustain a higher level of physical activity for longer periods of time than ectotherms is true. Endotherms, such as mammals and birds, regulate their body temperature internally through metabolic processes. They can maintain their metabolic rate and activity level high, regardless of the external temperature, by producing more heat or increasing blood flow to their body surface, as necessary. This biological feature allows endotherms to stay active even in cooler environments.
On the other hand, ectotherms depend on external sources of heat, such as the sun, to regulate their body temperature. Their activity level and metabolic rate are closely tied to the ambient temperature. Therefore, when it is cold, ectotherms have reduced metabolic activity, which directly affects their ability to sustain physical activity.
Through evolution, endothermy has provided a significant advantage in terms of sustained activity levels, particularly in varying and colder climates, which is not seen in ectotherms.