Which one of the following classes demonstrates double circulation of blood?

Double circulation is a characteristic of vertebrates where blood passes through the heart twice during one complete cycle through the body [1]. This system consists of two distinct circuits: the pulmonary circulation, which carries deoxygenated blood to the lungs, and the systemic circulation, which delivers oxygenated blood to the rest of the body [3]. While fishes possess a single circulation system with a two-chambered heart [1], tetrapods evolved more complex structures. Amphibians and most reptiles have a three-chambered heart that facilitates a form of double circulation, though it often involves some mixing of blood in a single ventricle. In contrast, mammals and birds possess a four-chambered heart that ensures complete separation of oxygenated and deoxygenated blood, representing the most efficient form of double circulation [2]. Therefore, among the given options, mammals are the definitive class demonstrating this advanced circulatory mechanism.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Oxygen enters the blood in the lungs > p. 92
2. [3] https://www.ncbi.nlm.nih.gov/books/NBK54112/
3. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC5696137/