2.8 The lungs and gas exchange
6 exam questions worth 13 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
0 / 13
Which is the correct order for the path of air into the lungs?
Choose one answer.
Correct Not quite: the answer is Trachea, bronchus, bronchiole, alveolus
Mark scheme
D
Model answer
D: trachea, bronchus, bronchiole, alveolus.
What is the job of the rings of cartilage in the trachea?
Mark scheme
to keep the trachea open / stop it collapsing (so air can flow)
Model answer
They hold the trachea open so it does not collapse and air can always pass through.
Oxygen moves from the air in the alveoli into the blood.
Name this process and explain why oxygen moves in this direction.
Mark scheme
- diffusion (1)
- oxygen concentration is higher in the alveoli than in the blood (1)
- so oxygen moves down its concentration gradient (1)
Model answer
The process is diffusion. The concentration of oxygen is higher in the air in the alveoli than in the blood, so oxygen moves down its concentration gradient into the blood.
Explain how a good blood supply helps gas exchange in the lungs.
Mark scheme
- blood carries oxygen away (quickly) / brings carbon dioxide (1)
- maintains a steep concentration gradient (1)
Model answer
The blood constantly carries oxygen away from the alveoli and brings more carbon dioxide, so a steep concentration gradient is maintained and diffusion stays fast.
Explain how the alveoli are adapted for efficient gas exchange.
Mark scheme
- many alveoli give a large surface area (1)
- thin walls / one cell thick (1)
- so short diffusion distance (1)
- good blood supply / many capillaries (1)
- maintains steep concentration gradient (1)
- moist (so gases dissolve) (1)
Maximum 4 marks
Model answer
There are millions of alveoli, which give a very large surface area. Their walls are only one cell thick, so the diffusion distance is short. Each alveolus has a good blood supply that carries oxygen away and keeps the concentration gradient steep. The alveoli are also moist, so gases dissolve before they diffuse.
Emphysema is a disease that destroys the walls between alveoli, so there are fewer, larger air spaces.
Suggest why people with emphysema become breathless easily.
Mark scheme
- smaller surface area (for gas exchange) (1)
- so less oxygen diffuses into the blood (for respiration) (1)
Model answer
The surface area of the lungs is reduced, so less oxygen can diffuse into the blood. Their cells get less oxygen for respiration, so they have to breathe faster.
Found a mistake?