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• There are three main gases in air that are taken in and removed from the body. These are oxygen, nitrogen and carbon dioxide.
• Gas exchange is the ‘swapping’ of gasses - absorbing oxygen into the blood and removing carbon dioxide from the blood.
• Diffusion moves oxygen out of the alveoli and into the blood.

• Inhalation and exhalation is the same as breathing or ventilation and is a physical process which moves air into and out of your lungs.
• Respiration is not the same as breathing, and is a chemical process which occurs in all of your cells.
• Gas exchange is a process that involves the swapping of gases that occurs at exchange surfaces such as the alveoli found within your lungs.

Gas exchange allows oxygen to travel into your cells for respiration whilst also removing carbon dioxide, which is a waste substance made by the process of respiration. Respiration is a vital process that involves releasing energy from glucose. All living things do this to stay alive.

The gas exchange system is made from key parts, each of which has a different function.

1. Air is breathed into the lungs through the windpipe called the trachea.

2. The trachea divides into two tubes called the bronchi.

3. The bronchi divides into many tubes called bronchioles.

4. The bronchioles divide until they end up in tiny air sacs called alveoli. There are millions of alveoli found within the lungs.

5. These alveoli are surrounded by a network of capillaries, allowing for oxygen and carbon dioxide to be exchanged between the blood in the capillaries and the air in the lungs. The oxygen molecules are carried in red blood cells.

6. The exchange of these two gasses occurs by a process called diffusion.

Alveoli are tiny air sacs in the lungs where gas is exchanged during breathing.

Within the human lungs the alveoli provide an efficient exchange surface adapted for gas exchange. This involves the ‘swapping’ of gasses. For example:

• Absorbing oxygen, which is needed for respiration, into the blood from the air.

• Transferring carbon dioxide, which is produced by respiration, from the blood into the lungs and then the air.

• Alveoli have a very large surface area to enable more diffusion of oxygen into the blood from the alveoli, and more carbon dioxide out of the blood into the alveoli.
• They are only one cell thick so that the diffusion distance is small.
• They have lots of blood capillaries to ensure a good blood supply to maintain concentration gradients of oxygen and carbon dioxide.
• They have moist surfaces for gases to dissolve in to form a solution to pass through the cell membrane.

Some water vapour is lost from the surface of the alveoli into the lungs - we can see this condensing when we breathe out on cold days.

Air gets into and out of the body by the physical process of breathing, also called ventilation. This process involves movements of the ribs, intercostal muscles and diaphragm to move air into and out of the lungs.

These are the changes involved during inhalation and exhalation.

Find out more about the process of breathing.

There are two types of respiration that can occur in your cells:

• Aerobic respiration
• Anaerobic respiration

Find out more about the two types of respiration.

Need some extra resources to support your biology lessons? In this short film from 91�ȱ� series Inside The Human Body viewers are taken on a journey around the Circulatory system.

91�ȱ� Teach has thousands of free, curriculum-linked resources to help deliver lessons - all arranged by subject and age group.