Cambridge (CIE) AS Your notes
Biology
The Gas Exchange System
Contents
The Human Gas Exchange System
Distribution of Tissues
Recognising Tissues
Recognising Structures
Structures & Functions of the Gas Exchange System
Gas Exchange Processes
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, The Human Gas Exchange System
Your notes
The Human Gas Exchange System
Gas exchange takes place in the human thorax. This is a collection of organs and tissues
in the chest cavity
The human gas exchange system diagram
The main structures of the human gas exchange system
Thorax structures table
Structure in Description
thorax
Trachea This airway leads from the mouth and nose to the bronchi. The trachea is
lined with mucus-secreting goblet cells and cilia. The cilia sweep
microorganisms and dust away from the lungs.
Lungs Humans have two lungs, both of which are a central part of the breathing
system and where gas exchange takes place.
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, Bronchi “Bronchi” is the plural of “bronchus”. The left and right bronchi are at the
bottom of the trachea and are similar in structure, but narrower. The
Your notes
bronchi lead to bronchioles.
Bronchioles These are narrow tubes (less than 1mm) which carry air from the bronchi to
the alveoli. As they are so narrow, they have no supporting cartilage and
so can collapse.
Alveoli The main site of gas exchange within the lungs. These are tiny sacs with
many structural adaptations to enable efficient gas exchange, such as
their thin walls and large surface area to volume ratio.
Capillary An extensive network of capillaries surrounds the alveoli and are an
network exchange surface between the lungs and the blood. During gas
exchange, oxygen diffuses from the alveoli and into the capillaries, while
carbon dioxide diffuses the other way and is exhaled.
Examiner Tips and Tricks
Remember to pay attention to command words in exams, as they will be asking
different things. For example, a question asking you to “Describe” the structure of the
alveoli is different from a question asking you to “Explain” the structure of the alveoli.
“Describe” questions are asking you to give an account of something or to write
events or processes in a logical order. “Explain” questions are asking you to write why
something happens or to link its structure to its function – as a result of this, “because”
will be an important part of your answer.
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Biology
The Gas Exchange System
Contents
The Human Gas Exchange System
Distribution of Tissues
Recognising Tissues
Recognising Structures
Structures & Functions of the Gas Exchange System
Gas Exchange Processes
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 1
, The Human Gas Exchange System
Your notes
The Human Gas Exchange System
Gas exchange takes place in the human thorax. This is a collection of organs and tissues
in the chest cavity
The human gas exchange system diagram
The main structures of the human gas exchange system
Thorax structures table
Structure in Description
thorax
Trachea This airway leads from the mouth and nose to the bronchi. The trachea is
lined with mucus-secreting goblet cells and cilia. The cilia sweep
microorganisms and dust away from the lungs.
Lungs Humans have two lungs, both of which are a central part of the breathing
system and where gas exchange takes place.
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 2
, Bronchi “Bronchi” is the plural of “bronchus”. The left and right bronchi are at the
bottom of the trachea and are similar in structure, but narrower. The
Your notes
bronchi lead to bronchioles.
Bronchioles These are narrow tubes (less than 1mm) which carry air from the bronchi to
the alveoli. As they are so narrow, they have no supporting cartilage and
so can collapse.
Alveoli The main site of gas exchange within the lungs. These are tiny sacs with
many structural adaptations to enable efficient gas exchange, such as
their thin walls and large surface area to volume ratio.
Capillary An extensive network of capillaries surrounds the alveoli and are an
network exchange surface between the lungs and the blood. During gas
exchange, oxygen diffuses from the alveoli and into the capillaries, while
carbon dioxide diffuses the other way and is exhaled.
Examiner Tips and Tricks
Remember to pay attention to command words in exams, as they will be asking
different things. For example, a question asking you to “Describe” the structure of the
alveoli is different from a question asking you to “Explain” the structure of the alveoli.
“Describe” questions are asking you to give an account of something or to write
events or processes in a logical order. “Explain” questions are asking you to write why
something happens or to link its structure to its function – as a result of this, “because”
will be an important part of your answer.
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