Question 40

Reptiles are characterized by bilateral symmetry, bony endoskeletons, and a dependence on external heat sources for regulating body temperature.

Reptiles exhibit bilateral symmetry, possess a bony endoskeleton, and rely on external environmental heat to regulate their body temperature, which is a key characteristic of ectothermic animals.

A) Insects

Insects do exhibit bilateral symmetry; however, they do not have a bony endoskeleton, as their skeletal structure is made of chitin. Additionally, insects are ectothermic but their body temperature regulation mechanisms differ from reptiles, which rely more heavily on external heat sources.

B) Sponges

Sponges are asymmetrical and lack a true skeletal structure, making them fundamentally different from animals with bilateral symmetry and bony endoskeletons. They do not regulate body temperature because they are aquatic organisms that do not have a nervous system or complex body structures.

C) Mammals

Mammals are characterized by bilateral symmetry and bony endoskeletons, but they are endothermic (warm-blooded) and do not depend on external heat sources for temperature regulation. This fundamental difference in thermoregulation disqualifies mammals from being the correct answer.

D) Reptiles

Reptiles possess bilateral symmetry and a bony endoskeleton. They are also ectothermic, meaning they rely on external heat sources to regulate their body temperature, aligning perfectly with the characteristics outlined in the question.

Conclusion

Reptiles are the only organisms listed that meet all specified criteria: they exhibit bilateral symmetry, possess a bony endoskeleton, and depend on external heat sources for thermoregulation. In contrast, insects, sponges, and mammals either lack a bony endoskeleton or do not rely on external heat sources, affirming that D is the definitive correct answer.