BREATHING

Objectives: To investigate the relationship between pressure and volume of a gas.To make and use a model of the chest, lungs, and diaphragm.To determine the limits of a model.

Materials:1 individual soda pop bottle or its equivalent with the bottom removed2 eight to twelve inch round helium quality balloons, one with the top removed

Background: There are three different types of models frequently used in science. There are mathematical models, conceptual (mental) models, and physical models. Mathematical models are the many equations used to help explain different natural phenomena. Some of equations are simple and others very complex. Mental models are the ideas that we have about how something works. Physical models are the most familiar. The physical models may be as simple as a diagram or as complex as a scale model of DNA or the solar system. No matter how good a model is it always has limits because it is not the real thing.

Procedure:1. Put a balloon on the top of the bottle as shown. Put the bottom half of a

balloon on the bottom of the bottle. 2. Study the part of your textbook and class notes that deal with breathing. Be

sure to study any drawings carefully.3. Use the model to make the balloon, “lung,” expand and collapse.

4. Try to model each of the following situations using the model you have constructed.

Some one inhaling and then exhaling.Someone choking on an object and then having the Heimlich maneuver performed.Someone with a torn diaphragm. Do not actually tear the balloon to illustrate this process.

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Questions:

1. What parts of the body do each part of the model represent? For example the opening of the bottle represents the mouth and nose.

2. What parts of the body are missing from the model?3. How did you represent someone choking?4. How did you represent the Heimlich maneuver?5. How is this model like the organs used in breathing in a human? How is it

different? 6. What limits does the model have?7. Draw and label a series of pictures to explain the changes in pressure and

volume that occur during breathing.8. Why are we using a model to investigate breathing?9. How might this model be improved? Explain why this suggestion is an

improvement.

Challenge Activities:1. In the nineteenth century doctors believed that men used their diaphragms to breathe

whereas women raised the ribs near the top of the chest. Finally, a woman doctor found that women only breathed this way because their clothes were so tight around their waists that they could not breathe normally. Some actually had their lower ribs removed surgically so they could wear even tighter clothes. Some women do this today. Construct an inexpensive working model that could be used to show the difference between the way men and fashionable women in the 1800’s breathed.

2. Construct an inexpensive working model that would show two lungs. 3. In larger insects and many other terrestrial arthropods many small tubes (tracheae)

extend from the outside of the animal to the interior cells. Construct an inexpensive working model of a tracheal system.

4. The lung does not have single membrane like a balloon. It is made of many small sacs (alveoli). Construct an inexpensive model that would more closely illustrate the structure of the lungs than the model used in this activity.

5. Think of some other things that happen to people involving lungs. Construct a model to illustrate one of these.

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6. A squid propels itself through the water by ejecting water. First, the squid takes water into its expanded mantle then it suddenly constricts the mantle. Design a model that illustrates this process and compare it to the pressure differences in the breathing process.

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BREATHINGTo the Teacher

Objective: To make and use a model of the chest, lungs, and diaphragm.To determine the limits of the model.

Materials:1 twelve-ounce soda pop bottle per student or its equivalent with the bottom cut off. A good pair of kitchen scissors will easily cut these bottles. Caution must be taken when cutting the bottles therefore students should not be allowed to cut the bottles.2 eight to twelve inch round helium quality balloons per student. Cut the top and stem off one. It is best to leave too much on the bottom half. Excess material can always be cut away. The bottom half of the balloon may be held in place with string or a rubber band if the balloon is too big.Extra balloons - If helium quality balloons cannot be purchased others will work, but they tear easily so you will need a much larger supply.

Procedure:This simple model encourages students to investigate and learn with little teacher intervention. Allow students to work with the model on their own. Discuss each of the questions in class before administering the summative assessment.

Questions:1. What parts of the body do each part of the model represent? For example the

opening of the bottle represents the mouth and nose. The bottle represents the rib cage. The balloon on the bottom models the diaphragm. The balloon on the top represents the lungs. The short neck of the balloon represents the trachea. Students may include other appropriate representations

2. What parts of the body are missing from the model? The model only has one lung. There is no back bone. Muscles and ribs in the rib cage are missing. The model lung has only one layer rather than many “alveoli.” Students may include other weaknesses in the model.

3. How did you represent someone choking? Student could put a wad of paper in the mouth of the bottle. They may find other ways to represent choking.

4. How did you represent the Heimlich maneuver? Quickly push up on the “diaphragm” or squeeze the bottle quickly. A slow push will not dislodge the material in the model or in reality.

5. How is this model like the organs used in breathing in a human? Moving the “diaphragm” down increases the volume of the “chest cavity,” just as the volume of the chest cavity is increased during inhalation. This causes lower pressure in the chest cavity and results in outside air pressure to push air into

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the “lung” of the model. How is it different? The "rib cage" is not as flexible as it is in the human system.

6. What limits does the model have? The model cannot actually exchange gasses, a necessary part of the breathing. Not all parts of the breathing system are accurately represented and many parts are missing.

7. Draw and label a series of pictures to explain the changes in pressure and volume that occur during breathing.

Be sure that students realize their drawings are models with many of the same limits as the bottle model. The drawings can use arrows to model the greatest air pressure something the bottle model cannot show directly. The drawings are limited more than the bottle because they do not actually move and they have only two dimensions.The expansion of the chest wall is what causes the actual decrease in air pressure in the chest cavity rather than a downward pull on the diaphragm.

Challenge activitiesStudents should be encouraged to invent their own models in these challenge activities. Each model should be accompanied by a brief statement of how the model is like and differs from the thing being modeled.

Sample summative assessment1. Make a big book explaining the breathing process. Use labeled diagrams to

help you explain the process.2. Write a short article for the school newspaper science section explaining how

models can be useful and how models are limited.3. Make an animated video explaining why a wound to the chest wall might

prevent breathing.

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4. Make a car bumper sticker explaining the relationship between volume and pressure of a gas.

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