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Difficulty: MediumVertebrates: Homoiothermic Classes (Aves and Mammalia)

Which of the following anatomical structures is uniquely present in mammals and actively contracts to expand the thoracic cavity during pulmonary ventilation?

  1. Muscular diaphragmAnswer
  2. B
    Four-chambered heart
  3. C
    Air sacs connected to lungs
  4. D
    Complete double circulatory system

Answer

The muscular diaphragm is the structure unique to mammals that contracts during pulmonary ventilation.
The muscular diaphragm is a dome-shaped sheet of muscle separating the thoracic cavity from the abdominal cavity found only in mammals. Its contraction flattens the dome, expanding the thoracic volume and pulling air into the lungs.

Step-by-Step Solution

1
Identify the respiratory ventilation mechanisms in homoiothermic vertebrates.
Mammals use a muscular partition separating the thoracic and abdominal cavities to create negative pressure for breathing.
This structure is absent in birds, which rely instead on rib cage movements and an air sac system.
2
Evaluate the choices for uniqueness to mammals.
The muscular diaphragm is found exclusively in Class Mammalia among vertebrates.
Structures like the four-chambered heart and complete double circulation are shared with Aves, while air sacs belong to Aves.

Key Concept

Distinguishing anatomical features of Class Mammalia compared to Class Aves
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Topics

Vertebrates: Homoiothermic Classes (Aves and Mammalia)

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