Final answer:
Ectotherms regulate temperature using environmental heat, whereas endotherms use internally generated heat to maintain a constant body temperature, allowing them to be active across varying environmental temperatures.
Step-by-step explanation:
The correct statement about endotherms and ectotherms is that ectotherms use external thermal energy to help regulate and maintain body temperatures, whereas endotherms rely on metabolically generated heat for the same purpose. Endotherms maintain a relatively constant body temperature regardless of environmental temperatures, which allows them to sustain a higher level of metabolic activity in cooler environments when compared to ectotherms. Ectotherms, on the other hand, often depend on environmental heat sources to regulate their body temperature, moving to warm or cool areas as needed to manage their internal temperature.
For example, reptiles, being ectotherms, may bask in the sun to increase their body temperature, while mammals, being endotherms, generate heat internally through metabolic processes, such as shivering, to regulate their body temperature on colder days. This capability to maintain a stable internal temperature provides endotherms with the advantage of functioning efficiently across a range of temperatures, whereas ectotherms are much more likely to be impacted by the environmental conditions.