Evaluating a breathing model
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2 .13
A group of students have been shown a model (Figure 1.2.13c) to help them understand how we breathe in and out. 4. In the model shown in Figure 1.2.13c, what represents each of the following?
glass tubing
a) the lungs
A
bung B
bell jar
b) the ribcage c) the diaphragm
balloons
d) the trachea 5. Describe what happens to the ‘lungs’ as the ‘diaphragm’ in this model moves down.
elastic membrane
6. Evaluate the model by listing ways in which the model matches a real breathing system and ways in which it doesn’t.
Under pressure
FIGURE 1.2.13c: You can make a model of the breathing system using a glass bell-jar and balloons.
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A difference between the pressure inside the lungs and the pressure of the air around us (atmospheric pressure) is what causes us to breathe in and out. •
When you breathe in, the pressure in your lungs falls below atmospheric pressure and air automatically rushes into the lungs.
•
When you breathe out, the pressure in your lungs rises above atmospheric pressure and air automatically rushes out of the lungs.
7. Describe when pressure in the lungs is at its highest and its lowest.
Did you know . . . ? Hiccups are caused by an involuntary contraction of the diaphragm. Hiccups are harmless and usually last only a few minutes. However, there are conditions under which hiccups persist for longer than a month.
8. Suggest what would happen if the pressure in the lungs stayed the same as atmospheric pressure. 9. The pressure in the lungs just before breathing in has been calculated as –0.4 kilopascals (kPa). The pressure in the lungs just before breathing out has been calculated as 0.4 kPa. Calculate the pressure difference in the lungs between breathing in and breathing out. (Remember to use units.)
Key vocabulary lungs diaphragm pressure
SEARCH: mechanism of breathing
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