Component 1: 1.2 The structure and functions of the cardio-respiratory system — Edexcel GCSE Physical Education
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Component 1: 1.2 The structure and functions of the cardio-respiratory system explained
The lungs sit in the thorax, protected by the ribcage.
Read the full explanation
The trachea divides into two bronchi, one entering each lung. Bronchi branch into smaller bronchioles, which end in clusters of alveoli where gas exchange occurs. The diaphragm is a dome-shaped muscle below the lungs. When the diaphragm contracts and flattens, and the external intercostals lift the ribs, the thorax volume increases and pressure falls, so air is drawn in. Oxygen in the alveoli diffuses into the blood, and carbon dioxide diffuses from the blood into the alveoli. When the diaphragm relaxes, thorax volume decreases and pressure rises, so air containing carbon dioxide is pushed out.
Your focus
- Identify the location of the lungs, bronchi, bronchioles, alveoli and diaphragm.
- Describe the role of each component in moving air into and out of the body.
- Explain how oxygen and carbon dioxide move between the alveoli and the blood.
Component 1: 1.2 The structure and functions of the cardio-respiratory system exam tips
Marking Points
- The lungs are located in the thorax and are protected by the ribcage.
- The trachea divides into two bronchi, one for each lung.
- Bronchi branch into smaller bronchioles.
- Bronchioles end in alveoli where gas exchange takes place.
- The diaphragm is a dome-shaped muscle below the lungs.
- Contraction of the diaphragm and external intercostals increases thorax volume and lowers pressure so air enters.
- Relaxation of the diaphragm decreases thorax volume and raises pressure so air leaves.
- Oxygen diffuses from the alveoli into the blood and carbon dioxide diffuses from the blood into the alveoli.
Examiner Tips
- 💡Learn the airway sequence trachea, bronchi, bronchioles, alveoli.
- 💡Use pressure changes to explain inspiration and expiration rather than saying the lungs suck or push.
- 💡Link each structure to its role in moving oxygen in and carbon dioxide out.
Common Mistakes
- Reversing the order of the airway: air passes through bronchi then bronchioles, not bronchioles then bronchi.
- Placing the diaphragm above the lungs: the diaphragm sits below the lungs.
- Saying the lungs push air out: air leaves because the diaphragm relaxes, thorax volume decreases and pressure rises.
- Confusing diffusion direction: oxygen moves into the blood and carbon dioxide moves into the alveoli.