Model of Lung

Feeling under pressure? Take a deep breath, relax and make yourself a third lung!

Australian Curriculum links

  • Science > Biological Sciences > Year 1 > ACSSU017
  • Science > Chemical Sciences > Year 5 > ACSSU077
  • Science > Biological Sciences > Year 8 > ACSSU150

You'll need

  • 600mL plastic bottle (with base cut off)
  • 2 round balloons (30 cm diameter)
  • plastic straw
  • rubber band
  • sticky tape
  • scissors
  • ball of plasticine (4 cm diameter)

Try this

Safety: An adult should cut the base from the plastic bottle.

  1. Use the scissors to remove the neck of one balloon. Stretch the balloon to fit it over the bottom of the bottle. Tape the edge of the balloon to the side of the bottle.
  2. Place one end of the straw into the other balloon. Attach the balloon to the straw using a rubber band.
  3. Make a hole through the plasticine. Push the straw through the hole. Allow at least 8 cm of the straw to extend above the clay. Gently squeeze the ball of clay to seal the clay around the straw.
  4. Place the balloon end of the straw into the bottle and use the clay to seal the opening of the bottle.
  5. Slowly pull down on and release the balloon at the base of the bottle. Observe the balloon inside the bottle and the air moving in and out of the straw.

What's happening?

In this model, the straw acts as an airway, the balloon inside the bottle acts as a lung, the stretched balloon acts as a diaphragm and the inside of the bottle acts as a chest cavity.

When you pull down on the ‘diaphragm’ balloon, the volume inside the bottle gets bigger. This decreases the air pressure inside the bottle so it is lower than the air pressure outside the bottle. Air flows from high pressure to low pressure, so air flows into the straw and fills the ‘lung’ balloon. When a person inhales, the diaphragm contracts and makes the volume of the chest cavity bigger. Air from outside enters the airways and fills the lungs.

When you let go of the ‘diaphragm’ balloon, the volume inside the bottle gets smaller. This increases the air pressure inside the bottle so it is higher than the air pressure outside the bottle. Air flows out of the ‘lung’ balloon through the straw. When a person exhales, the diaphragm relaxes and makes the volume of the chest cavity smaller. Air leaves the lungs and flows out of the airways.

The respiratory system is vital for survival. It works closely with the circulatory system to bring oxygen into the body and to remove carbon dioxide from the body. During inhalation, air containing oxygen moves into the lungs. The oxygen moves from the alveoli of the lungs into the capillaries of the circulatory system and the circulatory system transports the oxygen to the body’s cells.

The cells use oxygen to undergo cellular respiration, a process that converts chemical energy in nutrients to adenosine triphosphate (ATP). ATP can be used to power the cells’ activities. Cellular respiration creates carbon dioxide as a waste product. When carbon dioxide mixes with water it creates carbonic acid. Because cells don’t function well in an acidic environment, it’s important to remove the carbon dioxide. The carbon dioxide moves from the cells into the capillaries and travels via the circulatory system to the lungs. At the lungs, the carbon dioxide moves from the capillaries and into the alveoli of the lungs. During exhalation, this carbon dioxide is emitted from the body.

Real world links

In the early and mid-1900s, many people were infected with the poliovirus. The poliovirus attacked the central nervous system and could cause paralysis. In some cases, people’s diaphragms were paralysed, so they couldn’t breathe. The iron lung was a machine that helped people with paralysed diaphragms to breathe. This involved a person lying flat on their back with their body inside a chamber and their head lying on a stand outside of the chamber. Their neck was surrounded by a rubber collar that provided a seal to maintain a fully-pressurised environment inside the chamber. A pump was used to change the air pressure inside the chamber. As the air pressure inside the chamber changed, so too did the air pressure inside the person’s lungs. When the air pressure of the lungs was less than that of the outside air, air flowed into the person’s lungs via the person’s nose and mouth. When the air pressure of the lungs was more than that of the outside air, air flowed out of the person’s lungs and through the person’s nose and mouth. More information can be found at University of Virginia—Iron Lung website.