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, including 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 technology such as the heart-lung machine, which keeps patients alive during a heart transplant. Engineers are currently working on creating an implantable, artificial lung that would aid patients with serious lung disease. One of the ways 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 as 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 improperly 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 worked on developing an actual artificial lung that helps patients breathe while fighting off nasty infections. Aerospace engineers design the systems that help astronauts breathe easily during space flight.

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


bronchi: The 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 ribcage.

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


Before the Activity

  • Gather materials and make copies of the Lung Worksheet.
  • Drill 2 holes (just big enough for a straw to fit through) in each of the caps of the 2-liter bottles. (Note: 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 bottoms of each of the 2-liter bottles.

With the Students

  1. Peel off the label, if any, on the 2-liter bottle.
  2. Tell students that the 2-liter bottle represents the human chest cavity.
  3. Stick the two straws through the two holes of 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.

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 screw the lid on tightly.
  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. They now have a finished model of the lungs (see Figure 3); now it's time to make the lungs work!

Photo shows a 2-liter bottle with two straws sticking through the 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 is covering 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.)

Photo shows a 2-liter bottle with two straws sticking through the 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 is covering 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 Lung Worksheet


Troubleshooting Tips

When cutting off the plastic bottle bottom, make sure that the edges are as smooth as possible so it does not rip theballoon 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 demonstrate how the lungs work by using their project. 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 part of the body is damaged. (Answer: The lungs are unable to inflate and/or deflate if there is a leak in the chest cavity. The lungs cannot maintain the pressure difference.) Discuss with the class: What could engineers do to help fix a puncture in someone'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 that is attached to an oxygen supply. Have students create a drawing of a machine that could help their model lung "breathe" without having them pull down or push up on the lower balloon. Explain that this is how an engineer 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.


U.S. Department of Health and Human Services, National Institutes of Health, National Heart, Lung and Blood Institute, Diseases and Conditions Index, "How is Asthma Treated?" Accessed May 23, 2006. http://training.seer.cancer.gov/anatomy/respiratory
U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program, Training Website, Bronchi, Bronchial Tree, and Lungs, "Bronchi and Bronchial Tree." Accessed May 23, 2006. http://training.seer.cancer.gov/anatomy/respiratory/passages/bronchi.html
Wikipedia, The Free Encyclopedia, Wikipedia,com, Respiratory system. Accessed May 23, 2006. www.wikipedia.org


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.