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Explore How Lung Infection Influences Breathing

10 reviews


Active Time
30-45 minutes
Total Project Time
2-3 hours
Key Concepts
The lungs, infection, health
Sabine De Brabandere, PhD, Science Buddies


Have you ever coughed, felt short of breath because you were sick, or felt it was hard work to take a breath? Maybe you have watched someone gasping for air. At times, these events can feel scary! This activity explores how mucus and fluid in the lungs or airways changes our breathing using a simple lung model. It can help you understand why symptoms like coughing and being short of breath happen.

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.


  • Gelatin powder; if not available, use jelly
  • Corn syrup
  • Disposable empty transparent bottle (10-16 fluid ounces) made of hard plastic (such as a sports drink bottle)
  • Two balloons (8-inch balloons work well)
  • Utility knife
  • Scissors
  • Adult helper
  • Tools to prepare gelatin:
    • Saucepan
    • Water
    • Measuring spoons
    • Measuring cups
    • Small bowl
  • Optional: A second bottle and two more balloons to make a second identical lung model

Prep Work

Prepare the gelatin
  1. In a medium bowl, stir 1/4 cup boiling water into 1 teaspoon of gelatin. Stir for at least 2 minutes.
  2. Mix in 1/4 cup of cold water.
  3. Let rest for 2 hours or until firm.
  4. After the gelatin has set, use a fork to loosen it up. The gelatin should be solid but still wobbly.
Prepare your lung model
  1. Ask an adult to cut the plastic bottle. Cut off the bottle's bottom so that when a balloon hangs inside the bottle from the spout there is about 1/3 to 3/4 of an inch of empty space below the balloon.
  2. Place the cut bottle down on the wide opening. Lower a balloon into the bottle until only part of the balloon's neck sticks out. Fold the neck of the balloon over the top of the bottle. The balloon represents a lung.

  3. Turn the bottle over (keeping the balloon inside) so the bottle top rests on the table. In the next steps you will create and add the diaphragm to your model.
  4. Make a knot in the neck of the second balloon. At the opposite side of this balloon cut off about a third of the balloon so you are left with a wide opening.

  5. Stretch the wide opening of the cut balloon over the wide opening of the bottle. Pull the edges of the balloon far enough up the bottle so the balloon surface is gently stretched. Make sure that the knot is on the outside and located near the middle of the bottle opening.

  6. Like an inflated balloon our lungs are full of air after we take a deep breath. We have two lungs, which are enclosed in the ribcage. When you breathe in, air flows into your lungs. If you place your hands on your ribcage, you can feel it expand so the lungs can take up more space. When you breathe out, air flows out of your lungs, and you can feel the ribcage contract. The balloon inside the bottle is like one of your lungs.

  7. Hold the bottle so you can see the balloon inside (representing the lung). Gently pull down on the knot. Observe and then let the knot come back to its neutral position and gently push it in. If your balloon slips off, painters' tape on the rim of the bottle or taping or gluing the balloon to the bottle will help.
    Think about:
    What happens to the balloon inside the bottle? Does this resemble breathing? If so, which part resembles breathing in and which part resembles breathing out?
  8. If your balloon does not inflate and deflate, look if one of the balloons has a hole, replace that part of the model, and test the model again. If it still does not work, try a smaller balloon inside the bottle.
  9. Optional: Make a second lung model, identical to the first (same type of bottle cut off at the same height, same size balloons). Having two models helps you to directly compare an infected to a healthy lung.


Explore a healthy lung
  1. Repeat the inhaling (pull the knot back) and exhaling (push the knot in) steps of your model a few times.
    Think about:
    How far does the balloon inflate and deflate with each inhalation and exhalation? Can you make your model take a deep and a shallow breath?
  2. Compare the inhaling and exhaling movement of the balloon with the breath of a healthy person.
    Think about:
    Do you hear the movement of air in and out of the model? Do you feel you have to exert effort to make your model breathe?
  3. Mimic a cough. A cough is the body forcefully expelling air to get rid of something that caused irritation. During a cough you breathe in deeply but instead of air flowing out while the chest cavity contracts, your throat closes, and air builds up in the lungs first. When the throat opens, air flows out in a forceful way. To make your model cough, pull the knot back an extra bit to mimicking a deep inhale. Then, push the knot in fast to create a sudden release.
    Think about:
    Can you make your model cough?
Explore an infected lung
  1. When lungs or airways (the pipes transporting air to the lungs) are infected, fluid and/or mucus can accumulate in them.
    Think about:
    How do you think that might change breathing?
  2. When you have two identical models, use one to model an infected lung and the other to compare the infected lung with the healthy one.
  3. We will use gelatin to mimic mucus in an infected lung. Break up the gelatin if you have not yet done so.
  4. Take ½ teaspoon of gelatin, place it on the mouth of the bottle, and let the model breathe in forcefully by pulling the knot back quickly. The goal is to suck the gelatin into the neck of the balloon. If the gelatin is not sucked in, try pulling the knot more forcefully, and if the gelatin is sucked into the body of the balloon, try pulling back a little slower until you have some gelatin stuck into the neck of the balloon.

  5. Gelatin stuck in the neck of the balloon mimics mucus getting stuck in the airways. Repeat the inhaling (pull the knot back) and exhaling (push the knot in) steps of your model with the neck of the balloon partially obscured by the gelatin. Listen and watch.
    Think about:
    Do you hear air being sucked in? What type of breathing does the sound remind you off? How is this different from the breathing in your healthy model?
  6. Mucus can trap viruses, bacteria and other irritants. A cough can help remove the mucus and the trapped irritants. Mimic a cough as described in step 3.
    Think about:
    Can you make your model cough up the gelatin?

  7. Sometimes, the lining of the airways is not just covered with extra mucus but also swollen.
    Think about:
    How would that compare to having mucus stuck in the airways?
  8. It any gelatin got stuck in the neck or body of the balloon, remove it as it will interfere with the next part of the activity. You can also use a new balloon to model the lung.
  9. Pour a teaspoon of corn syrup in the balloon. Remove the balloon with the knot and rub one side of the body of the balloon against the other side so the body of the balloon (the inside of the lung) is well coated. The body of the balloon usually sticks together after this action, that is fine. If a pool of corn syrup collects at the bottom of the balloon, turn the model over and let some corn syrup drip out.

  10. In infected lungs, irritation and inflammation can lead to mucus, fluids and debris filling the lungs. The corn syrup coating of the body of the balloon mimics this situation. Have your model breath in and out a few times. Listen and watch how the model breathes.
    Think about:
    Does the breathing sound different compared to the breathing of a healthy model? Does the balloon inflate and deflate as much as it did when the balloon was empty? Do you feel you have to pull harder to let your model take a breath?
  11. Sometimes the airways and the lungs are inflamed, and mucus and fluid are present in the airways and lungs. Keep the corn syrup coating in the body of the balloon and add some gelatin to the neck of the balloon so the airways are almost completely blocked. Have your model breath in and out a few times. Listen and watch how the model breathes.
    Think about:
    How does this breathing compare to the breathing of a healthy model?
  12. Let this infected lung cough.
    Think about:
    Is it easy to cough up the gelatin when the body of the balloon is coated with corn syrup?
  13. We breathe to provide our body with oxygen.
    Think about:
    What do you think happens when we can only breath in a small volume of air? How much fresh oxygen do you think an infected lung can inhale in comparison to a healthy lung?


Discard the balloon of the infected lung model after a day or two.

What Happened?

When you pulled the knot back, your balloon filled up with air. In the same way, when the diaphragm in our body pulls back, air flows into our lungs, and we inhale. When you pushed the knot in, the space inside the bottle decreased, and the balloon probably deflated. In the same way, when the diaphragm relaxes the chest cavity decreases, and air is pushed out of the lungs, and we exhale.


When you pulled and pushed the knot further the balloon inflated and deflated more. This mirrors what happens when a bigger volume of air is displaced when we breathe more deeply.

When gelatin got stuck in the neck of the balloon, you probably heard air being sucked in. In a similar way, when mucus or swelling obstructs the airways, wheezing occurs. Coughing can help reduce or remove the obstruction.

When the balloon was coated with corn syrup and the sides stick together, you might have noticed that you had to work harder to fill the balloon with air. Similarly, patients with fluid and mucus in the lungs need to work harder to fill their lungs with air. You probably also observed that parts of the balloon no longer moved up and down with each breath, they did not take part in the breathing. Parts of the lungs of patients that suffer from fluid or excess mucus in their lungs are also no longer available for breathing. For those patients, the amount of oxygen that can be taken up by the blood in each breath has decreased.

Digging Deeper

Allergies, asthma, viral infections such as COVID-19, smoking, bacteria, and many other things can cause inflammation in the airways and lungs. Inflammation causes swelling, and worse, fluid, debris and mucus might build up in the respiratory system—the collection of organs that take part in breathing. Some amount of mucus is normal as it keeps the lungs from drying out. The body creates more mucus when it senses irritants, viruses and bacteria, so it can trap them and cough them up, and thus remove the unwelcome substances. But too much mucus or fluids in the lungs causes problems. It can make breathing difficult and decreases the area in the lungs where carbon dioxide in blood can be exchanged with freshly inhaled oxygen, making it harder for your body to adequately oxygenate the blood. Thus, it effectively makes parts of the lungs incapable of performing its task. Mucus can also clog airways leading to wheezing. Other symptoms might range from a general feeling of irritation and uneasiness to laborious breathing, and general fatigue. Mucus and fluids in the lungs can be treated. Depending on the case and severity, home remedies, lifestyle changes, medication, chest physiotherapy are some of the treatment options for mild cases. It is important to get medical help for prolonged and severe cases.

Inflammation is a reaction of the body to fight off a foreign organism, but when the immune system overreacts, more problems arise. It can lead to permanent lung damage. The walls of the air-sacks—the place where gas-exchange with the blood (carbon dioxide exchange for oxygen) takes place—become thick and unable to function. Just like in the case of mucus, debris or fluid in the lungs, patients experience a decrease in oxygen level in the blood, they feel fatigued and might have laborious breathing. They might breath faster and heart rate might go up in an effort of the body to increase the amount of oxygen in the blood. In severe cases, it can lead to acute respiratory distress syndrome (ARDS). ARDS is serious and patients need intensive care to support respiration.

Persons who have lung damage or other lung conditions, or people with a compromised immune system are more susceptible to developing major problems when their airways or lungs are infected. It is essential for this group to prevent infection.

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For Further Exploration

  • To model swollen airways, change the way the balloon that mimics the lung is attached to the mouth of the bottle. Try your best to make the opening small, like a slit and observe how it changes the breathing.

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