BioEd Online

Teacher Background

Each of us breathes about 8 to 10 times per minute. When we exercise, the rate increases to 15 to 20 times per minute. Surprisingly, our lungs have no muscles of their own. How, then, is the work of breathing done?

The diaphragm and rib muscles of the chest wall work for the lungs. By changing the size of the chest cavity, these muscles control whether air enters or exits the lungs.

The diaphragm, a broad, thin muscle that stretches across the body between the chest and the abdomen, is responsible for about 75% of the airflow in breathing. At rest, the diaphragm actually bulges upward. When we are about to take a breath of air, or inhale, the diaphragm moves downward, thereby increasing the space available (and decreasing total pressure) within the chest. The rib muscles move upward and outward at the same time, increasing the space available for airflow by another 25%. Outside air rushes in to fill this space.

Breathing out, or exhaling, is normally a passive process. As the muscles of the chest and diaphragm relax, the space inside the chest becomes smaller and air moves out of the lungs. When we exhale forcibly, some of these muscles actively help push the air out.

Objectives and Standards

Concepts

• Air moves in and out of the lungs in response to volume changes in the chest cavity.

Science, Health, and Math Skills

• Predicting

• Observing

• Modeling

• Drawing conclusions

Materials and Setup

Teacher Materials (see Setup):

• half-liter water bottles (12 for groups of 2; 6 for groups of 4)

• clear plastic packaging tape

Materials per Group of Students or per Student

• 2 balloons, 9-in. round

• pair of scissors

• prepared bottle

Setup

1. One or more days before beginning this activity, ask each student (or group of students) to bring a small- to medium-sized clear plastic bottle from home (half-liter water or soft drink bottle, or liquid dishwashing detergent bottle).
   
   Note. Liter-size soft drink bottles are too large to work effectively in this activity.

2. Cut off and discard the bottom third of each bottle. The remaining top part of the bottle should be about six inches (15 cm) tall.

3. Cover sharp edges with clear plastic packaging tape.

Procedure and Extensions

1. Begin by asking each student to notice his or her own breathing. Ask, How many times are you breathing per minute? How can you tell? Which parts of your body move when you breathe? Tell students that they will make a simple model to investigate how air moves in and out of the body.

2. Have the Materials Managers pick up prepared plastic bottles and balloons for their groups.

3. One student from each group should slide a balloon into the top of the bottle and roll the open end (mouth) of the balloon over the top edge of the bottle.

4. Another student should cut off the bottom of the second balloon and tie a knot in the stem (mouth) of the remaining piece. While one student holds the bottle, another should slide the cut end of the balloon around the cut end of the bottle.

5. Ask students to predict what might happen when the bottom balloon is pulled downward. Have students try pulling the bottom balloon gently. Ask, What happened to the top balloon? Point out that this is similar to what happens when each of us breathes in.

6. Next, direct the students to squeeze the sides of the bottle gently while pushing the bottom balloon into the space in the bottle. Ask, What happened?

7. Using the diagram on page 8 of the Air unit’s Explorations magazine, help students understand that the balloon inside the model represents our lungs and that the bottom balloon represents our diaphragm. Discuss ways in which their models are similar to and different from the actual respiratory system.

8. Have students stand and take a deep breath. They should be able to notice that their chests expand when they inhale and contract when they exhale.

Extensions

• Challenge your students to make their lung models “cough” or “sneeze.” For a more dramatic effect, place 1/2 teaspoon of baking soda or baby powder inside the balloon “lung” before making the model “cough” or “sneeze.”
  
  Safety Note: Be aware of risks to students with respiratory illnesses, such as asthma.

• You may prefer to have students make their breathing machines at home with a family member or friend (see the Air unit’s Explorations magazine, p. 4).

• Try making a more accurate model by filling the inside of the breathing machine with water.

Handouts and Downloads