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Difficulty: MediumCirculatory and Transport Systems in Animals

An anatomical examination of a vertebrate heart reveals two distinct atria and a single ventricle partially divided by an incomplete muscular septum. To which group of animals does this organism belong, and how does this cardiac structure affect its circulatory system?

  1. A
    Amphibians, resulting in a single circulatory pathway where deoxygenated blood bypasses the lungs entirely.
  2. Non-crocodilian reptiles, resulting in a double circulation system where oxygenated and deoxygenated blood partially mix within the ventricle.Answer
  3. C
    Bony fishes, resulting in a single circulation system where oxygenated blood is pumped directly from the ventricle to systemic capillaries.
  4. D
    Birds, resulting in a double circulation system where oxygenated and deoxygenated blood are kept completely separate during cardiac contraction.

Answer

Non-crocodilian reptiles possess a heart with two atria and a single ventricle partially divided by an incomplete septum, which results in partial mixing of oxygenated and deoxygenated blood during double circulation.
Non-crocodilian reptiles (such as lizards, snakes, and turtles) feature a three-chambered heart with two atria and a single ventricle partially divided by an incomplete muscular septum. This structural arrangement facilitates double circulation while permitting partial mixing of oxygenated and deoxygenated blood within the ventricle.

Step-by-Step Solution

1
Analyze the given anatomical heart structure
The organism has two atria and one ventricle containing an incomplete septum.
Identifying chamber count and septal features allows classification among vertebrate classes.
2
Compare chamber count across vertebrate groups
Fish have 2 chambers (1 atrium, 1 ventricle); Amphibians have 3 chambers without a septum; Reptiles (except crocodilians) have 3 chambers with an incomplete septum; Birds and Mammals have 4 chambers with a complete septum.
An incomplete septum inside a single ventricle is unique to non-crocodilian reptiles.
3
Determine the functional circulatory consequence
Double circulation is present, but because the ventricular partition is incomplete, partial mixing of oxygenated (from lungs) and deoxygenated (from body) blood occurs.
The incomplete septum reduces but does not completely eliminate blood mixing prior to pulmonary and systemic ejection.

Key Concept

Comparative Vertebrate Heart Structure and Circulation Pathways
Estimated Time:1m 0s
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Topics

Circulatory and Transport Systems in Animals

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