The Sarcopterygian Heart Had Two Atria and a Partially Divided

question 42

Multiple Choice

The sarcopterygian heart had two atria and a partially divided ventricle.Modern amphibians have two atria and an undivided ventricle.This seems like an evolutionary step backwards,but it is not.All of the following statements help us understand why the undivided ventricle is adaptive for amphibians except one.

• A)Because gas exchange occurs in the skin of amphibians, venous return of blood to the right side of the amphibian heart is often comprised of oxygenated blood.
• B)When an amphibian is submerged, its lungs are not in use.Blood returning to the right side of the heart and leaving the undivided ventricle can be shunted away from the lungs.
• C)Blood from the left atrium can bypass the ventricle and go directly into the conus arteriosus and the systemic circulation.
• D)Even though we don't understand how it occurs, the spiral valve in the conus arteriosus helps send less oxygenated blood from the right side of the heart to the lungs and more highly oxygenated blood from the left side of the heart to the systemic artery and the rest of the body.This situation is most likely to occur when the amphibian is on land.

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