Breathing
The breathing system, breathing and respiration, tests on exhaled air, choking and smoking.
Offline pages
Saved on this device only. Connect at least once every 30 days to confirm Premium. Sign-out or a change of account removes saved copies.
Before you begin
Breathing moves air into and out of the lungs, where oxygen passes into the blood and carbon dioxide leaves it. This topic explains how the diaphragm and ribcage move air, how breathing differs from respiration, how to test inhaled and exhaled air, and how choking and smoking affect the airways and lungs.
Be comfortable with: the idea that air moves from a place of higher pressure to a place of lower pressure.
Learning goals
- Breathing and respiration
- Respiratory parts and functions
- Inhaled and exhaled air
- Carbon-dioxide test
- Water-vapour test
- Choking
- Smoking and passive smoking
Syllabus statements covered
- describe the roles of breathing and respiration in keeping humans alive
- identify the following parts of the respiratory system and state their functions: windpipe, bronchi, lungs, diaphragm and ribcage
- explain the differences in the composition of inhaled and exhaled air
- use simple tests for: — carbon dioxide (limewater test)
- use simple tests for: — water vapour (cobalt chloride paper test) [knowledge of detailed procedures of tests is not required]
- explain how choking affects breathing
- state the effects of smoking and passive smoking on the respiratory system (e.g. bronchitis, lung cancer)
Lessons
Work through them in order.
- Breathing and respirationExplain how the diaphragm and ribcage draw air into the lungs, and how breathing differs from respiration.
- Compare inhaled and exhaled airCompare inhaled and exhaled air using limewater and cobalt chloride paper.
- Choking and smokingExplain how airway blockage affects breathing and how smoking and passive smoking raise respiratory disease risks.
Practise and check
Or choose
Topic reference
Quick reference
| Breathing in | Breathing out (at rest) | |
|---|---|---|
| diaphragm | contracts and flattens | relaxes, becomes dome-shaped |
| ribcage | up and out | down and in |
| chest volume | increases | decreases |
| air | flows in | flows out |
| Test for | Use | Positive result |
|---|---|---|
| carbon dioxide | limewater | turns milky |
| water vapour | dry blue cobalt chloride paper | turns pink |
Core knowledge to remember
- Air travels through the windpipe and bronchi to the lungs, where gas exchange takes place.
- Breathing moves air; respiration releases energy from food in every living cell.
- Exhaled air has less oxygen, more carbon dioxide and more water vapour than inhaled air.
- Choking blocks the airway, so oxygen cannot reach the blood.
- Smoking and passive smoking increase the risk of bronchitis and lung cancer.
Common mistakes
- Using “respiration” to mean breathing.
- Saying the lungs move air by themselves.
- Saying exhaled air contains no oxygen.
- Giving a gas test without its positive result.
- Saying smoking only harms the smoker.