Gas exchange surfaces
Swapping gases
- Your cells need oxygen and must get rid of carbon dioxide.
- Gas exchange swaps these gases by diffusion.
- It happens across the huge surface of the lungs.
Practice
Gases move across the gas-exchange surface by:
Oxygen and carbon dioxide are exchanged by diffusion down their concentration gradients.
A good exchange surface
- a large surface area — more gas can cross at once.
- a thin surface — a short distance to diffuse.
- a good blood supply — keeps a steep concentration difference.
- good ventilation — fresh air keeps the difference steep.
Practice
A good gas-exchange surface has which features? (Choose all that apply.)
Large area, thin surface, good blood supply and good ventilation — a thick wall would slow diffusion.
The breathing system
| Part | Job |
|---|---|
| trachea | the windpipe; carries air to the lungs |
| bronchi | two tubes, one to each lung |
| bronchioles | smaller branching tubes |
| alveoli | tiny air sacs where gas exchange happens |
- Each alveolus is wrapped in capillaries; there are millions of them (huge area), walls one cell thick (short distance), good blood supply.
- (Supplement) Rings of cartilage hold the trachea open.
Practice
Put the air path in order, from throat to gas exchange.
Air flows trachea → bronchi → bronchioles → alveoli.
Practice
Alveoli are well adapted because there are millions of them with walls one cell thick.
Millions of thin-walled alveoli wrapped in capillaries give a huge area and short diffusion distance.
You've got it
Key idea
- a good gas-exchange surface is large, thin, with a good blood supply and good ventilation
- air path: trachea → bronchi → bronchioles → alveoli
- alveoli = millions of sacs, one cell thick, wrapped in capillaries — ideal for diffusion