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Difficulty: MediumCirculatory and Transport Systems in Animals

During a laboratory examination of circulatory structures across different vertebrate groups, a specimen is observed to have a three-chambered heart comprising two separate atria and a single undivided ventricle. Oxygenated blood from the lungs and deoxygenated blood from the rest of the body enter separate atria before undergoing partial mixing in the single ventricle. To which of the following vertebrate classes does this specimen belong?

  1. ReptiliaAnswer
  2. B
    Pisces
  3. C
    Aves
  4. D
    Mammalia

Answer

Reptilia
The class Reptilia (along with Amphibia) features a three-chambered heart made up of two atria and one ventricle. Blood returning from the lungs enters the left atrium and blood from systemic tissues enters the right atrium; both empty into the single ventricle where partial mixing of blood occurs before ejection.

Step-by-Step Solution

1
Analyze the anatomical features given in the stem
The heart has two atria, one ventricle (3 chambers total), and shows partial mixing of oxygenated and deoxygenated blood.
Identifying the number of chambers and mixing pattern narrows down the vertebrate class.
2
Compare chamber count with vertebrate circulatory configurations
Pisces have 2 chambers (1 atrium, 1 ventricle); Amphibians and Reptiles have 3 chambers (2 atria, 1 ventricle); Birds (Aves) and Mammals have 4 chambers (2 atria, 2 ventricles).
Vertebrate classes have evolutionary trends in heart chamber complexity.
3
Select the class matching a three-chambered heart configuration
Reptilia is the only option listed that features a three-chambered heart.
Reptiles match the described anatomical structure.

Key Concept

Comparative Vertebrate Heart Chamber Configurations
Estimated Time:1m 0s
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Topics

Circulatory and Transport Systems in Animals

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