2.6 Breathing: gas exchange
Summary: The transfer of gases between an organism and its environment is called gas exchange. For example, when you breathe in, you take in oxygen, and when you breathe out, you give out carbon dioxide. 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 process of gas exchange
- describe how parts of the gas exchange system are adapted to their function
- compare inhaled and exhaled air.
Think back
- What is an organ system?
- What do your lungs do?
- Where in the cell does Respiration take place?
Key idea The transfer of gases in body systems is called gas exchange.
Key words gas exchange, lungs, ribcage, trachea, alveolus, inhale, exhale, pie chart
The transfer of gases between an organism and its environment is called gas exchange. For example, when you breathe in, you take in oxygen, and when you breathe out, you give out carbon dioxide.
What happens when we breathe?
Gas exchange takes place inside your lungs. Lungs are made of soft tissue that expands when you breathe in – this allows you to take in lots of oxygen. Your lungs are protected by your ribs. These are hard and strong bones that make up your ribcage. Figure 1 shows your ribs and lungs.
Figure 1You can see your lungs and ribs on a chest X-ray.
A Name the organ where gas exchange takes place in humans.
Figure 2 shows the main parts of your gas exchange system (respiratory system). Follow the arrows with your finger to see how air travels through your mouth and nose to your lungs, where oxygen in the air moves by Diffusion into your blood. The blood then carries the oxygen to all the Cells in your body.
Figure 2Air has to travel from your mouth and nose to your lungs for you to get oxygen into your blood. Full text alternative to the content
There are millions of alveoli (singular: alveolus) in your lungs. They create a large surface area. They have thin walls that are only one cell thick. These features help gas exchange occur quickly and easily.
Why do we breathe in and out?
When you breathe in, you inhale to take in oxygen. The oxygen is used in respiration to transfer Energy. Respiration produces carbon dioxide. This needs to be removed from the body. When you breathe out, you exhale to remove carbon dioxide.
The amount of oxygen your body needs determines how fast you will breathe. You need larger amounts of oxygen when you exercise. This is because your cells respire more to transfer more energy to your body cells.
B Suggest what happens to your breathing rate when you start running.
The pie charts in Figure 3 show how much of each gas is present in inhaled air and exhaled air.
Figure 3These pie charts show the amounts of each gas in inhaled air and exhaled air. Full text alternative to the content
C Use the pie charts to identify the gas in air which is not used by the body.
The air you breathe out is a much higher temperature than the air you breathe in because it has been warmed by the body. It also contains water vapour. Water is a waste product of respiration.
Maths skills The pie charts in Figure 3 show the gases in inhaled air and exhaled air. Why is this the best chart to use? Would another type of graph be better?
Stretch zone
- Copy and complete Table 1 to show the differences between inhaled air and exhaled air. Use the words less, more, same, hotter, and colder. Words can be used once, more than once, or not at all. Table 1Inhaled Exhaled oxygen carbon dioxide temperature water vapour
- Describe how the ribcage is adapted to perform its function.
Stretch zone
- Explain two ways alveoli are adapted for gas exchange.