Hands-on Activity: Just Breathe

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

A drawing of the human chest cavity showing the clavicle, vertebrae, ribs and lungs.
Figure 1. The human chest cavity.
Copyright © National Institute of Standards and Technology, Advanced Technology Program http://www.atp.nist.gov/eao/sp950-2/eai_1.jpg


Students explore the inhalation/exhalation process that occurs in the lungs during respiration. Using everyday materials, each student team creates a model pair of lungs.

Engineering Connection

By studying the respiratory system, engineers have created technologies such as the heart-lung machine, which keeps patients alive during heart transplants. Engineers are currently working on creating an implantable, artificial lung to aid people with serious lung diseases. One way that engineers study complicated systems is by creating models, similar to how students create their own model lungs in this activity.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

Suggest an alignment not listed above

Learning Objectives

After this activity, students should be able to:

  • Describe the function of the respiratory system.
  • Create a model of the lungs and explain what happens to them when you inhale and exhale.
  • Give examples of engineering advancements that have helped with respiratory systems.

Materials List

Each group needs:

  • 2-liter empty plastic bottle with cap
  • 2 plastic drinking straws; available inexpensively at restaurant supply stores or donated by fast-food chains; do not use the flexible drinking straws
  • 2 9-inch balloons
  • 1 larger balloon; for example, for a punch ball
  • 2 rubber bands
  • Lung Worksheet, one per student


Have you ever been on a crowded subway or bus? You probably could not wait to get out where there were not so many people and you could move around freely. This is similar to the process that causes air to flow in and out of your lungs. The air molecules are either crowded outside (in the environment) and want to get into the lungs where there are less air molecules (inhalation), or they want to get outside because they are too crowded inside the lungs (exhalation).

When you inhale, your diaphragm muscle contracts downward and rib muscles pull upward causing air to fill the lungs. Can you think of why? Well, when your diaphragm moves down and ribs move up, they make more space in your chest (in the thoracic cavity) for air. This also decreases the pressure on your lungs so the air will flow in from the outside. The opposite happens when you breathe out. Your diaphragm relaxes and the ribs and lungs push in which causes air to be pushed out.

Engineers need to understand the respiratory process in order to design machines and medicines to help people whose respiratory systems function incorrectly or with difficulty. Have you ever known someone who suffers from asthma or pneumonia? Well, chemical engineers design devices and medicines, such as inhalers filled with an adrenergic bronchodilator to help people breathe better. Engineers have also developed artificial lungs that help people breathe while fighting off infections. And engineers also design the systems that help astronauts breathe easily during space flight, when they are far away from the Earth's atmosphere.

Engineers use models to study complicated processes and better understand them. In this activity, you will act like engineers by building models of the lungs in order to study the breathing process and what happens when you breathe in and out.


bronchi: Two large tubes connected to the trachea that carry air to and from the lungs.

diaphragm: A shelf of muscle extending across the bottom of the rib cage.

lungs: Spongy, saclike respiratory organs that occupy the chest cavity, along with the heart. They provide oxygen to the blood and remove carbon dioxide from it.


Before the Activity

  • Gather materials and make copies of the Lung Worksheet.
  • In each of the 2-liter bottle caps, drill 2 holes that are just big enough for a drinking straw to fit through. Tip: Make sure to drill the holes far enough apart that the holes do not become one big hole!
  • Using a pair of scissors, cut off the bottom of each 2-liter bottle.

With the Students

  1. Peel off the labels, if any, on the 2-liter bottles.
  2. Tell students that the 2-liter bottle represents the human chest cavity.
  3. Stick two drinking straws through the two holes in the bottle cap.
  4. Place one 9-inch balloon on the end of each straw and secure them with rubber bands, as shown in Figure 2.

A photo shows two straws sticking through the cap of a 2-liter bottle. At the ends of each straw is a green balloon, held on by a rubber band.
Figure 2. Example model "lungs" created for the experiment setup.
Copyright © 2005 Teresa Ellis, ITL Program, University of Colorado Boulder

  1. Tell students that the straws represent the bronchi and the balloons represent the lungs.
  2. Stick the balloon ends of the straws through the bottle opening and tightly screw on the lid.
  3. Stretch out the larger balloon and place it over the open bottom of the bottle.
  4. Tell students that this larger balloon represents the diaphragm. Now they have a finished model of the lungs! (See Figure 3,) Next, it is time to make the lungs work!

A photo shows a 2-liter bottle with two straws sticking through its screw-on cap. A balloon is held onto the ends of each straw with a rubber band. The bottom of the bottle has been cut off and a third, larger balloon covers the opening.
Figure 3. A model of the lungs.
Copyright © 2004 Teresa Ellis, University of Colorado Boulder

  1. Pull the diaphragm (balloon) down (that is, away from the lungs) in order to inflate the lungs. (Note: This makes the chest cavity larger and decreases the pressure.)
  2. Push the diaphragm (balloon) in (towards the lungs) in order to deflate the lungs. (Note: This makes the chest cavity smaller and increases the pressure.)

A photo shows a 2-liter bottle with two straws sticking through its screw-on cap. A balloon is held onto the ends of each straw with a rubber band. The bottom of the bottle has been cut off and a third, larger balloon covers the opening. A person's hand is pushing up on this bottom balloon to deflate the lungs.
Figure 4. A model of the human chest cavity.
Copyright © 2005 Teresa Ellis, University of Colorado Boulder

  1. Have students complete the worksheet.
  2. To conclude, have teams make presentations of their model lungs, as described in the Assessment section.


Troubleshooting Tips

When cutting off the plastic bottle bottom, make sure that the edges are as smooth as possible so it does not rip the balloon on the bottom. If edges are rough, bind them with masking or duct tape.

Seal any potential leaks with poster tack.


Pre-Activity Assessment

Discussion Questions: Solicit, integrate and summarize student responses.

  • How do the lungs work? How do you inhale and exhale?
  • Does your breathing change when you exercise? How?

Activity Embedded Assessment

Worksheet: Have students record their observations and complete the Lung Worksheet. Review their answers to gauge their mastery of the subject.

Post-Activity Assessment

Presentation and Informal Discussion: Have one or more groups use their projects to demonstrate how the lungs work. Next, hypothesize with the class: What would happen to the respiratory system if we punctured it? Have one group puncture the cavity (bottle) or diaphragm (rubber bottom) and demonstrate what happens to the lungs if this body part is damaged. (Answer: The lungs are unable to inflate and/or deflate if the chest cavity has a leak. The lungs cannot maintain the pressure difference.) Discuss with the class: What could engineers do to help fix a puncture in a person's lungs?

Activity Extensions

Have students research respiratory diseases and how they affect the function of the respiratory system. Can they alter their model to show what happens to the lungs with these diseases? Can they demonstrate on their models what has been done to help people with respiratory problems?

Engineers have developed an artificial lung to help people fight infection. The artificial lung is approximately 18-inches long and consists of membranes that pass oxygen to the blood and remove carbon dioxide. It is inserted through a vein in the leg and lodged in the main vein (the vena cava) passing blood to the heart. The blood is re-oxygenated through a catheter attached to an oxygen supply. Have students create a drawing of a machine that could help their model lungs "breathe" without having them pull down or push up on the lower balloon. Explain that this is how engineers might begin to develop life-saving machines.

Activity Scaling

For lower grades, have students make one lung rather than two. Use a smaller water bottle rather than a 2-liter bottle and one balloon lung rather than two.


"How is Asthma Treated?" Diseases and Conditions Index, National Heart, Lung and Blood Institute, National Institutes of Health, U.S. Department of Human Services. Accessed May 23, 2006. http://training.seer.cancer.gov/anatomy/respiratory

"Bronchi and Bronchial Tree." Training Website: Bronchi, Epidemiology and End Results (SEER) Program, U.S. National Cancer Institute's Surveillance. Accessed May 23, 2006. http://training.seer.cancer.gov/anatomy/respiratory/passages/bronchi.html

"Respiratory system." Wikipedia, The Free Encyclopedia, Wikipedia,com. Accessed May 23, 2006. https://en.wikipedia.org/wiki/Respiratory_system


Teresa Ellis; Malinda Schaefer Zarske; Janet Yowell


© 2006 by Regents of the University of Colorado

Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder


The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. 0338326). However, these contents do not necessarily represent the policies of the DOE or NSF, and you should not assume endorsement by the federal government.

Last modified: October 16, 2016