Theory:

Breathing mechanism:
The mechanism of breathing can be understood by a simple model.
 
Materials required:
1. Plastic bottle - 1
2. Balloons - 3
3. Y shaped tube - 1
4. Cork
 
Procedure:
  • Take a wide plastic bottle and make an incision in the middle of the bottle.
  • Use some tools to make a hole in the cork and fix the one end of the Y shaped tube.
  • To the forked end of the tube fix two deflated balloons.
  • Introduce the tube into the bottle and seal it to make it air tight.
  • Seal the open base of the bottle with the help of a thin rubber of plastic sheet with the help of a large rubber band.
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Construction of lung model
  
Working mechanism:
  • To understand the working mechanism of lungs hold the large, bottom balloon and pull it downwards slowly.
  • Now push the rubber/plastic sheet up and observe the balloons.
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Observation:
  
From this model we can conclude that when we pull down the balloons inflate and deflate, due to pressure inside the bottle similar to the lungs.
  
Inference:
  
On comparing this model with our respiratory system we can infer that the balloons represent the lungs, the bottle represents the thorax and the rubber sheet represents the diaphragm.
  
The comparison of bottle lung model with human respiratory system:
  
Thoracic cavity
Bottle lung model
This cavity filled with pleural fluidBottle filled with air
Trachea is flexibleY-shaped tube is rigid
Diaphragm flattensBalloon drawn downwards
Lungs made of alveoliBalloons empty
Ribs moves and changes the thoracic cavity volume
Bottle does not move