Which animal group has a four-chambered heart with complete separation of blood?

Which animal group has a four-chambered heart with complete separation of blood?

• A. Birds
• B. Reptiles
• C. Amphibians
• D. Fish

Answer: (A)

Complete separation of blood by a four-chambered heart enables fully separate pulmonary and systemic circuits, which high-demand activities like sustained flight rely on. Birds have two atria and two ventricles, so oxygenated blood returning from the lungs stays on the left side to nourish the body, while deoxygenated blood on the right is pumped to the lungs. The two streams do not mix, keeping arterial oxygen content high and supporting a high metabolic rate. Other groups differ: fish have two heart chambers; amphibians typically have three with some mixing in a single ventricle; most reptiles have three chambers with incomplete separation (crocodilians are an exception with a four-chambered heart). Among the options, birds best exemplify a four-chambered heart with complete separation of blood.

Complete separation of blood by a four-chambered heart enables fully separate pulmonary and systemic circuits, which high-demand activities like sustained flight rely on. Birds have two atria and two ventricles, so oxygenated blood returning from the lungs stays on the left side to nourish the body, while deoxygenated blood on the right is pumped to the lungs. The two streams do not mix, keeping arterial oxygen content high and supporting a high metabolic rate. Other groups differ: fish have two heart chambers; amphibians typically have three with some mixing in a single ventricle; most reptiles have three chambers with incomplete separation (crocodilians are an exception with a four-chambered heart). Among the options, birds best exemplify a four-chambered heart with complete separation of blood.