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Exam questions · Biology · The Circulatory System

The Lungs and Gas Exchange

  • 7 exam questions
  • 19 marks
  • 8 quick checks
  1. 1 Name [3 marks]

    Figure 1 shows the lungs. Name the parts labelled A, B and C.

    The lungs with three parts marked A, B and C.
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    Model answer

    A is the trachea. B is a bronchus. C is the alveoli (air sacs).

    Mark scheme

    • A: trachea — 1 mark
    • B: bronchus — 1 mark
    • C: alveoli — 1 mark
  2. 2 State [2 marks]

    Name the two gases exchanged in the alveoli and state the direction each one moves.

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    Model answer

    Oxygen moves from the alveoli into the blood. Carbon dioxide moves from the blood into the alveoli.

    Mark scheme

    • Oxygen from the alveoli into the blood — 1 mark
    • Carbon dioxide from the blood into the alveoli — 1 mark
  3. 3 Explain [2 marks]

    Explain why the walls of the alveoli are only one cell thick.

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    Model answer

    A thin wall gives a short diffusion path. Oxygen and carbon dioxide can therefore diffuse across quickly.

    Mark scheme

    • Short diffusion path — 1 mark
    • Faster diffusion of gases — 1 mark
  4. 4 Explain [3 marks]

    Explain why oxygen diffuses from the alveoli into the blood.

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    Model answer

    The concentration of oxygen is higher in the air in the alveoli than in the blood. Oxygen therefore diffuses down the concentration gradient. The gradient is kept steep by breathing and by the blood carrying oxygen away.

    Mark scheme

    • Higher concentration of oxygen in the alveoli — 1 mark
    • Diffuses down the concentration gradient — 1 mark
    • Gradient kept steep by ventilation / blood flow — 1 mark
  5. 5 Calculate [2 marks]

    A person takes 15 breaths per minute. Each breath takes in 400 cm³ of air. Calculate the volume of air breathed in per minute.

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    Model answer

    400 × 15 = 6000 cm³ per minute.

    Mark scheme

    • 400 × 15 — 1 mark
    • 6000 cm³ per minute — 1 mark
  6. 6 Explain [4 marks]

    Explain how the lungs are adapted for gaseous exchange.

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    Model answer

    The lungs contain millions of alveoli, which give a very large surface area. The walls of the alveoli and capillaries are one cell thick, so the diffusion path is short. A rich supply of blood in the capillaries carries oxygen away and brings carbon dioxide, keeping the concentration gradient steep. Breathing ventilates the alveoli, which also keeps the gradient steep.

    Mark scheme

    • Millions of alveoli give a large surface area — 1 mark
    • Walls one cell thick, short diffusion path — 1 mark
    • Rich blood supply keeps the gradient steep — 1 mark
    • Ventilation keeps the gradient steep — 1 mark
  7. 7 Explain [3 marks]

    A person has emphysema, a disease that destroys the walls of the alveoli. Explain why this person feels short of breath.

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    Model answer

    Destroying the walls reduces the surface area of the alveoli. Less oxygen can diffuse into the blood. The body cells therefore receive less oxygen for respiration, so the person feels short of breath.

    Mark scheme

    • Reduced surface area — 1 mark
    • Less oxygen diffuses into the blood — 1 mark
    • Less oxygen for respiration in cells — 1 mark

Quick check

  1. 1

    What are the tiny air sacs in the lungs called?

    1. ABronchi
    2. BBronchioles
    3. CAlveoli
    4. DCapillaries
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    C: Alveoli

    Alveoli are the air sacs where gases are exchanged with the blood.

  2. 2

    Which gas diffuses from the blood into the alveoli?

    1. AOxygen
    2. BCarbon dioxide
    3. CNitrogen
    4. DWater only
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    B: Carbon dioxide

    Carbon dioxide is at a higher concentration in the blood arriving at the lungs, so it diffuses into the alveoli.

  3. 3

    What is the trachea?

    1. AThe windpipe
    2. BA blood vessel
    3. CAn air sac
    4. DA muscle
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    A: The windpipe

    The trachea is the windpipe, which carries air from the mouth and nose to the bronchi.

  4. 4

    How many cells thick is the wall of an alveolus?

    1. ATen
    2. BFive
    3. CTwo
    4. DOne
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    D: One

    The wall is one cell thick, which gives a short diffusion path.

  5. 5

    Which feature of the lungs keeps the concentration gradients steep by moving air?

    1. AThe thin walls
    2. BThe large surface area
    3. CVentilation
    4. DThe capillary wall
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    C: Ventilation

    Ventilation, or breathing, moves fresh air in and stale air out.

  6. 6

    What surrounds each alveolus?

    1. AA layer of muscle
    2. BA network of capillaries
    3. CA layer of fat
    4. DA bronchus
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    B: A network of capillaries

    A network of capillaries brings blood past the alveolus for gas exchange.

  7. 7

    A person breathes 20 times a minute and takes in 300 cm³ each time. What volume do they breathe in per minute?

    1. A15 cm³
    2. B320 cm³
    3. C600 cm³
    4. D6000 cm³
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    D: 6000 cm³

    300 × 20 = 6000 cm³ per minute.

  8. 8

    Why do the lungs have millions of alveoli?

    1. ATo give a large surface area
    2. BTo make the lungs heavier
    3. CTo slow down the blood
    4. DTo warm the air
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    A: To give a large surface area

    Many alveoli give a very large surface area for gas exchange.