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Modeling Breathing

As you breathe, your body moves air into and out of your lungs. All body movements depend on muscles, which work only by contracting. How does your body use muscles to cause air to flow into and out of your lungs? In this investigation, you will make a working model of human lungs that will help you answer this question.

Problem 

How do muscle contractions move air into and out of the lungs?

Materials 

  • small, clear plastic bottle

  • large round balloon

  • small round balloon

  • one-hole rubber stopper

  • scissors

Skills 

Using Models

Design Your Experiment 


    Part A: A Model of Normal Lungs

  1. Place a clear plastic bottle on its side. Press one point of a pair of scissors through the side of the bottle about 1 cm from the bottom.

  2. Using the scissors, cut off the bottom of the bottle by cutting all the way around. Trim off any rough spots from the edge.

  3. Stretch a small balloon, and blow it up several times to make it pliable.

  4. Pull the opening of the small balloon over the bottom of a one-hole rubber stopper.

  5. Insert the balloon through the mouth of the bottle. Press the stopper tightly into the bottle so that it holds the lip of the balloon in place.

  6. Stretch a large balloon, and blow it up several times to make it pliable.

  7. Using the scissors, cut off about 1 cm from the rounded, closed end of the large balloon. Tie the other end closed.

  8. Stretch the large balloon far enough over the cut end of the bottle to keep the balloon from slipping off, as shown below.


  9. As you watch the small balloon, pull down on the knot of the large balloon. Then, still watching the small balloon, press up on the large balloon.


    10. Part B: A Model of a Chest Injury

  10. Formulating Hypotheses If a person receives an injury that punctures the skin and muscles of the chest, outside air can come into direct contact with the outer surfaces of the lungs. How would such an event affect a person's ability to breathe? Record your hypothesis.

  11. Think of a way you could modify your model of human lungs to represent the lungs in a person with a punctured chest. Write a description of your plan, including your prediction of how the alternative model will behave and how the model will test your hypothesis.

  12. Show your plan to your teacher. If your teacher approves, make a model of a punctured chest. Use your model to test your hypothesis.

Analyze and Conclude 

  1. Observing In Part A, what happened to the small balloon in your model when you pulled down on the large balloon?

  2. Observing What happened to the small balloon when you pressed up on the large balloon?

  3. Inferring What happened to the pressure inside the bottle when you moved the large balloon up and down?

  4. Formulating Hypotheses What caused the small balloon in Part A to expand and contract?

  5. Using Models Do you consider the model you made in Part A an adequate representation of the human respiratory system? Explain.

  6. Drawing Conclusions In Part B, how did your alternative model represent a chest injury? What does that model show about the role of the chest wall in breathing?

  7. Evaluating In Part B, was your prediction correct? Did the behavior of your second model support your hypothesis? Explain your answer.

  8. Drawing Conclusions How do muscles cause air to flow into and out of human lungs?

  9. SAFETY Explain how you demonstrated safe practices as you used sharp objects such as scissors.

Making Models  Obtain information from a hospital, doctor's office, or county health department about the mechanics of breathing and diseases such as asthma and emphysema that make breathing difficult. Find out what causes these diseases, how they affect breathing, and how they are prevented and treated. Then, make a new model that demonstrates the effects of one of these diseases. Be prepared to explain how well your model represents that disease.
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