Structure of the Breathing System (Edexcel IGCSE Biology: Double Science)
Revision Note
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Structure of the Breathing System
- The lungs are the gas exchange surface in humans
- All gas exchange surfaces have features in common which allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time
- They include:
- Large surface area to allow faster diffusion of gases across the surface
- Thin walls to ensure diffusion distances remain short
- Good ventilation with air so that diffusion gradients can be maintained
- Good blood supply to maintain a high concentration gradient so diffusion occurs faster
Structures in the human breathing system
Breathing Structures Table
Cilia and mucus
- The passages down to the lungs are lined with ciliated epithelial cells
- Cilia cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed
- The mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet, or cup
- The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them from getting into the lungs and damaging the cells there
Mucus traps particles, dust and pathogens and cilia beat and push it up and away from the lungs
Exam Tip
You may notice that several of the features of alveoli that make them suited to their function are the same as those that make villi suited to their function or root hair cells suited to their function – the reason for this is because all of these structures are involved in transporting substances across their surfaces – by diffusion, active transport, osmosis or a combination.So if you learn the features for one, you also know many of the features of the others!
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