What type of organism usually requires external sources for thermoregulation?

Ectotherms are organisms that rely primarily on external environmental sources to regulate their body temperature. Unlike endotherms, which generate sufficient internal heat through metabolic processes to maintain a constant body temperature, ectotherms depend on their surroundings to heat or cool themselves. This means that ectotherms like reptiles and amphibians often bask in the sun to raise their body temperature or seek shade or water to cool down.

In contrast, endotherms, such as mammals and birds, possess mechanisms to create their own body heat, allowing them to maintain a stable internal temperature regardless of external conditions. Vertebrates encompass both ectothermic and endothermic organisms, while somatic cells refer to non-reproductive cells in multicellular organisms and are not related to thermoregulation in the context of organisms as a whole. Understanding the differences between these categories clarifies why ectotherms are specifically characterized by their reliance on external sources for thermoregulation.