How do our lungs fill with air when we breathe? In this hands-on biology project, you will make a simple working model of the human lungs using balloons, a straw and a transparent plastic cup.
This model helps students understand the basic role of the lungs, windpipe and diaphragm during breathing.
By completing this activity, students will be able to:
Understand how air moves into and out of the lungs.
Explore the role of the diaphragm in breathing.
Identify the lungs, windpipe and chest cavity in a simple model.
Observe how changes in air pressure make the balloon inflate and deflate.
You will need:
Transparent plastic cup or glass
Balloons
Drinking straw
Rubber band
Scissors
Tape or modelling clay, if needed for sealing
Attach a small balloon securely to one end of the straw. Make sure there are no gaps through which air can escape.
The balloon will represent a lung, while the straw will represent the windpipe or trachea.
Insert the balloon and straw into the transparent plastic cup. The balloon should remain inside while the other end of the straw stays outside.
Seal the area around the straw so that outside air cannot enter through any gaps.
Cut another balloon and stretch it tightly across the open side of the plastic cup. Secure it with a rubber band.
This flexible balloon sheet represents the diaphragm.
Gently pull the diaphragm balloon downward. The balloon inside the cup should inflate.
Now push the diaphragm upward or allow it to return to its original position. The balloon inside should deflate.
When you pull the lower balloon downward, the space inside the cup increases. This lowers the air pressure inside the model, causing air to enter through the straw and inflate the balloon lung.
When the lower balloon moves upward, the space inside becomes smaller. Air is pushed out through the straw, causing the balloon lung to deflate.
In the human body, the diaphragm contracts and moves downward when we inhale. This creates more space in the chest cavity and allows the lungs to expand. During exhalation, the diaphragm relaxes and moves upward, helping air leave the lungs.
| Model Part | Human Body Part |
|---|---|
| Plastic cup | Chest cavity |
| Balloon inside the cup | Lung |
| Straw | Trachea or windpipe |
| Balloon stretched across the opening | Diaphragm |
This activity is a simplified representation of breathing. A real human respiratory system contains two lungs, branching bronchial tubes, millions of tiny air sacs called alveoli, ribs and several muscles.
The lungs themselves do not actively pull air inside. Changes in chest-cavity volume and air pressure allow air to move into and out of them.
If the balloon does not inflate:
Check for air leaks around the straw.
Make sure the balloon is tightly attached to the straw.
Ensure the diaphragm balloon completely covers the opening.
Pull the lower balloon slowly and evenly.
Check that the straw is not blocked or bent.
Ask an adult to help when using scissors or making holes in the plastic cup.
Keep balloons away from children under three years old because broken or uninflated balloons can present a choking hazard. Do not inhale through the straw while it is connected to the model.
Make the model and investigate these questions:
What happens when you pull the diaphragm farther downward?
Does the balloon inflate if there is a small air leak?
What happens when the straw is partially blocked?
Can you modify the model to include two balloon lungs?
Record your observations and explain how each change affects the movement of air.
Watch the Pakistan Science Club video, build your own working lung model and explore the science of breathing through a simple hands-on experiment.