Gas exchange surfaces
Introduced| English | Meaning |
|---|---|
| gas exchange/ɡæs eksˈtʃeɪndʒ/ | The movement of gases, such as oxygen and carbon dioxide, between an organism and its environment or between internal regions. |
| alveoli/ˈælvɪɒli/ | Tiny air sacs in the lungs where gases are exchanged between air and blood. |
Trading gases with the air
- Every cell needs oxygen and must get rid of carbon dioxide.
- This swap happens at a gas exchange 气体交换 surface — and good ones share key features.
Which are features of a good gas exchange surface? (Select all that apply.)
Difficulty 2/5 · 140 coins + a small bonus on first completion today
A thick, dry surface would slow diffusion.
A large ______ area speeds up the diffusion of gases.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
More surface area means faster gas exchange.
Features of a good surface
- Large surface area, thin (short diffusion distance), moist, and a good blood supply.
- These features make diffusion of gases fast.
Gas exchange happens across the huge surface of the lungs
A good gas-exchange surface
Tap the alveolus to see the four features that make it ideal for exchange: a huge surface area, a thin wall, a moist lining and a good blood supply.
Gas exchange in the lungs happens in the:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Alveoli are the tiny air sacs where gases exchange.
The alveoli 肺泡
- In the lungs, gas exchange happens in millions of tiny air sacs called alveoli.
- Their huge combined surface area and thin walls make them ideal.
At an alveolus, oxygen diffuses into the blood and carbon dioxide diffuses out
At the alveoli, oxygen diffuses:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Oxygen moves down its gradient into the blood.
Gas exchange occurs by diffusion, which is different from breathing.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Breathing ventilates; gas exchange is diffusion across the surface.
How gases move
- Oxygen diffuses from the alveoli into the blood; carbon dioxide diffuses the other way.
- A steep concentration gradient (kept by breathing and blood flow) speeds this up.
Gas exchange is diffusion, not breathing. Breathing moves air in and out; gas exchange is the diffusion of O₂ and CO₂ across the alveolar surface. They work together but are different processes.
Expired air has less oxygen and much more carbon dioxide than inspired air
You've got it
- a good gas exchange surface is large, thin, moist with a good blood supply
- the alveoli provide a huge surface area and thin walls
- oxygen diffuses in, carbon dioxide diffuses out — driven by a concentration gradient
Write from oxygen at an alveolus
- Blood arriving at an alveolus is low in oxygen.
- The air in the alveolus is high in oxygen.
How does the oxygen move, and which features help?
The gradient decides the direction.
How does oxygen enter the blood at an alveolus?
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Oxygen moves down its concentration gradient.