Class IX Practical: Animal Life - Breathing Mechanism (Bell Jar Experiment)

Objective

To demonstrate the mechanism of breathing (inhalation and exhalation) using a bell jar model and compare it with human lungs.

Guidelines

1. Model Setup: Observe the bell jar model of the human respiratory system. It typically consists of:
   • A bell jar (representing the thoracic cavity).
   • A Y-shaped tube (representing trachea and bronchi).
   • Two balloons (representing lungs) attached to the Y-tube.
   • A rubber sheet (representing the diaphragm) tied to the open end of the bell jar.
2. Demonstration of Inhalation: Pull the rubber sheet (diaphragm) downwards. Observe what happens to the balloons.
3. Demonstration of Exhalation: Push the rubber sheet (diaphragm) upwards. Observe what happens to the balloons.
4. Comparison with Human Lungs: Relate the movements in the model to the actual process in human breathing:
   • Pulling diaphragm down -> diaphragm contracts and moves down, increasing thoracic volume -> air rushes into lungs (inhalation).
   • Pushing diaphragm up -> diaphragm relaxes and moves up, decreasing thoracic volume -> air is forced out of lungs (exhalation).
5. Discussion: Explain the role of pressure changes in the thoracic cavity during breathing.

Expected Outcome

Clear understanding of the physical mechanism of breathing, demonstrating how changes in thoracic volume and pressure lead to air movement into and out of the lungs.