CHEN SCIENCE
T
I
K
HOME-MADE LUNGS
RECIPE
WHAT YOU WILL NEED
A plastic bottle
A straw
An elastic band
Scissors
2 balloons
Playdough
1. Remove the bottom of your
bottle
2. Tie a knot in one end of a
balloon and snip of the fat end
3. Stretch this end around the
bottom of your plastic bottle
4. Put a straw in the neck of the
other balloon and secure
tightly with the elastic band
but not so that you crush the
straw.The air must flow
through so test it with a little
blow through the straw to see
if the balloon inflates
5. Put the straw and the ballon
into the neck of the bottle and
secure with the playdough
making a seal around the
bottle – make sure that again,
you don’t crush straw.
This homemade lung is a great representation of how our lungs work. When we breathe in, the intercostal
muscles between our ribs contract which causes the ribcage to come out and upwards. The diaphragm
contracts and that causes it to flatten, these two processes increase the volume of the chest cavity. As a
result, the atmospheric pressure in the lungs will be lowered so that air will move from outside the lung
(higher pressure) to inside the lung (lower pressure). You can replicate this by pulling the balloon at the
bottom of the bottle and you will notice that the balloon inside inflates.
The opposite happens when you breathe out –your ribcage comes back in because your intercostal
muscles relax, your diaphragm also relaxes which causes it to curve back up and so you decrease the
volume in the chest cavity. This causes the pressure in the chest cavity to increase so air is forced out.
You can replicate this by pushing the balloon at the bottom of the bottle inwards which will cause the
balloon inside to deflate.
Why do we even need lungs in the first place anyway? Microorganisms, such as bacteria, can exchange
gases through diffusion. However, as an organism gets bigger and bigger, diffusion is not as efficient.
Hence why multicellular organisms like animals and plants will need specialised organs for certain
processes. For us, our lung’s only job is to make sure we get enough oxygen for other bodily
processes and to get rid of carbon dioxide. The lung has the following characteristics that
allow us to do this efficiently:
• Alveoli have a large surface area
• Good blood supply in the alveoli
• Thin air sacs for quick diffusion of gases – oxygen diffuses into the blood, carbon dioxide diffuses out of
the blood
• Moist air sacs, which means that gases can dissolve
How can you take it further?
• This can be scaled up to a bell jar demonstration that involves two balloons.
• Why not find out how good your lungs are? Compare lung capacity with your friends by finding out how
big a balloon can be blown up with just one breath. If you find balloons difficult to blow up, you can use
long and thin plastic bags.