2.5 Breathing: lungs
Summary: Even when you are sitting still, your ribcage is moving. This allows your lungs to fill with oxygen and is essential for you to stay alive. Tags: science oxford-science student-book-7 biology Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
- describe the changes that happen when a person inhales and exhales
- describe how a bell jar can be used to model breathing
- describe a method used to measure lung volume.
Think back
- Why do you inhale?
- What happens in the alveoli?
- What is Diffusion?
Key idea The lungs expand and relax during breathing.
Key words diaphragm, lung volume, asthma
Even when you are sitting still, your ribcage is moving. This allows your lungs to fill with oxygen and is essential for you to stay alive.
How do you breathe?
When you breathe, muscles in your chest get shorter. They contract. Figure 1 shows a bell-jar model. This model can show you what is happening inside your lungs when you breathe in and out. The jar represents your chest. The balloons represent your lungs. The rubber sheet represents a muscle called the diaphragm.
Figure 1This bell-jar model can be used to represent breathing. Full text alternative to the content
What happens when you inhale?
Figure 2 shows what happens in your body when you inhale. It shows the same process in the bell-jar model.
Figure 2Inhaling in the lungs and in the bell-jar model. Full text alternative to the content
A List the two changes that increase the volume inside your chest when you breathe in.
What happens when you exhale?
Figure 3 shows what happens in your body when you exhale. It shows the same process in the bell-jar model.
Figure 3Exhaling in the lungs and in the bell-jar model. Full text alternative to the content
B List the two changes that decrease the volume inside your chest when you breathe out.
How can we measure lung volume?
Figure 4 shows how you can measure your lung volume using a plastic bottle. When you breathe out into the plastic tube, air from your lungs takes the place of the water in the bottle. If you breathe out as much as you can, the volume of water pushed out of the bottle is equal to how much air your lungs can hold.
Figure 4You can measure your lung volume by breathing into a bottle.
Regular exercise can help increase your lung volume. A large lung volume means that more oxygen can enter your body. Smoking, diseases such as asthma, and old age can reduce lung volume.
Working scientifically How big are your lungs? Calculate your own lung volume. Breathe as hard as you can into a 3-litre bottle of water. Suggest why your doctor would not use this method to find your lung volume. Think about how accurate (correct) the value is.
Stretch zone
- Copy and complete Table 1. Use the words up and out, down and in, down, up, decreases, increases. Table 1Action Inhaling Exhaling ribs move diaphragm moves chest volume
- Describe how you could measure the lung volume of an athlete.
Stretch zone
- The bell-jar model works in the same way as the lungs. Describe how a bell-jar model can be used to represent inhalation.Suggest one problem with the model.