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Difficulty: HardCirculatory and Transport Systems in Animals

In an experiment comparing the circulatory efficiency of different vertebrate groups, physiological measurements show that non-crocodilian reptiles achieve a higher degree of systemic arterial oxygenation than adult amphibians, despite both groups possessing a three-chambered heart. Which anatomical feature of the non-crocodilian reptilian heart is primarily responsible for reducing the mixing of oxygenated and deoxygenated blood?

  1. The presence of an incomplete muscular septum partially dividing the single ventricleAnswer
  2. B
    The complete division of the atrium into distinct left and right chambers
  3. C
    The presence of a four-chambered heart with two completely isolated ventricles
  4. D
    The total absence of a sinus venosus in the reptilian circulatory system

Answer

The presence of an incomplete muscular septum partially dividing the single ventricle
Although both amphibians and non-crocodilian reptiles have three-chambered hearts (two atria and one ventricle), the reptilian ventricle contains an incomplete muscular septum. This partial wall creates functional sub-chambers during contraction, directing oxygen-rich blood from the left atrium into the systemic aortic arches and oxygen-poor blood from the right atrium into the pulmonary artery, thereby reducing blood mixing and delivering higher oxygen levels to systemic tissues.

Step-by-Step Solution

1
Analyze the heart anatomy of adult amphibians.
Adult amphibians have a 3-chambered heart consisting of two atria and one completely undivided ventricle, leading to significant mixing of oxygenated and deoxygenated blood.
Establishing baseline circulatory anatomy for amphibians.
2
Compare amphibian ventricular structure with non-crocodilian reptilian ventricular structure.
Non-crocodilian reptiles also possess a 3-chambered heart (two atria and one ventricle), but their ventricle features an incomplete internal muscular septum.
Identifying the key anatomical difference between the two vertebrate classes.
3
Relate the partial septum to physiological efficiency.
During ventricular contraction, the partial septum acts as a dynamic partition that channels oxygenated blood into the systemic aorta and deoxygenated blood toward the pulmonary artery, significantly reducing blood mixing compared to amphibians.
Explaining how structural adaptation improves systemic oxygen delivery.

Key Concept

Comparative vertebrate heart structures and partial ventricular separation in reptiles
Estimated Time:1m 30s
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Topics

Circulatory and Transport Systems in Animals

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