Monotremes have which heart type?

Monotremes have which heart type?

• A. Three-chambered heart
• B. Four-chambered heart
• C. Five-chambered heart
• D. No heart

Answer: (B)

Monotremes have a four-chambered heart. This means there are two atria and two ventricles that are fully separated, keeping oxygen-poor blood from mixing with oxygen-rich blood. Blood returns from the body to the right atrium, moves to the right ventricle, and goes to the lungs to get oxygen; then it returns to the left atrium, passes into the left ventricle, and is pumped to the rest of the body. This complete separation supports efficient circulation, which is a hallmark of mammals and birds. In contrast, three-chambered hearts (seen in many amphibians and non-crocodilian reptiles) involve some mixing of blood and are less efficient. No heart is obviously incorrect in animals that don’t have a heart, but monotremes clearly do. So the correct heart type is four chambers.

Monotremes have a four-chambered heart. This means there are two atria and two ventricles that are fully separated, keeping oxygen-poor blood from mixing with oxygen-rich blood. Blood returns from the body to the right atrium, moves to the right ventricle, and goes to the lungs to get oxygen; then it returns to the left atrium, passes into the left ventricle, and is pumped to the rest of the body. This complete separation supports efficient circulation, which is a hallmark of mammals and birds. In contrast, three-chambered hearts (seen in many amphibians and non-crocodilian reptiles) involve some mixing of blood and are less efficient. No heart is obviously incorrect in animals that don’t have a heart, but monotremes clearly do. So the correct heart type is four chambers.