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Difficulty: Very hardVertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

In poikilothermic vertebrates, circulatory pathways show evolutionary progression to accommodate respiratory adaptations. Which of the following statements correctly contrasts the path of deoxygenated blood entering the heart in an adult amphibian with that in a bony fish (Class Pisces)?

  1. In adult amphibians, deoxygenated blood from the body enters the right atrium before reaching the single ventricle, whereas in bony fish, deoxygenated blood flows sequentially through the sinus venosus, atrium, and ventricle.Answer
  2. B
    In adult amphibians, deoxygenated blood from systemic circulation enters the left atrium, whereas in bony fish, deoxygenated blood enters a two-chambered ventricle directly from the gills.
  3. C
    In adult amphibians, deoxygenated blood is pumped into a four-chambered heart with complete septation, whereas in bony fish, deoxygenated blood bypasses the heart and flows directly to systemic organs.
  4. D
    In adult amphibians, deoxygenated blood bypasses the atrium completely into the conus arteriosus, whereas in bony fish, deoxygenated blood is received by a three-chambered heart consisting of two atria and one ventricle.

Answer

In adult amphibians, deoxygenated blood from the body enters the right atrium before reaching the single ventricle, whereas in bony fish, deoxygenated blood flows sequentially through the sinus venosus, atrium, and ventricle.
Bony fish (Pisces) have single circulation where a two-chambered heart (one atrium, one ventricle, preceded by the sinus venosus) handles exclusively deoxygenated blood. Adult amphibians (Amphibia) possess a three-chambered heart with double circulation; deoxygenated blood returning from the body tissues enters the right atrium, while oxygenated blood enters the left atrium.

Step-by-Step Solution

1
Analyze the circulatory architecture of Class Pisces (bony fish).
Fish have a single-circuit heart through which only deoxygenated blood flows. Systemic venous blood returns to the sinus venosus, moves to the single atrium, then to the single ventricle, and finally into the conus/bulbus arteriosus toward the gills.
Fish exhibit single circulation where all blood passing through the heart is deoxygenated.
2
Analyze the circulatory architecture of adult Class Amphibia.
Amphibians exhibit double circulation with a three-chambered heart (two atria and one undivided ventricle). Deoxygenated systemic blood enters the right atrium via the sinus venosus, while oxygenated blood from the lungs/skin enters the left atrium. Both empty into the single ventricle.
Dual atrial entry separates systemic return (deoxygenated) from pulmonary/cutaneous return (oxygenated).
3
Compare the option statements against these structural anatomical facts.
The option stating that amphibian deoxygenated blood enters the right atrium while fish deoxygenated blood passes through the sinus venosus, atrium, and ventricle is completely accurate.
It correctly identifies the receiving chambers and path of deoxygenated blood in both poikilothermic classes.

Key Concept

Comparative Vertebrate Circulatory Systems (Pisces vs Amphibia)
Estimated Time:1m 30s
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Topics

Vertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

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