1. 1
   A biology teacher described the alveoli in human lungs as tiny air sacs, extremely numerous, each with an extremely thin wall and a rich network of surrounding blood capillaries, adapted to allow efficient exchange of gases with the blood.

   (a)

   Which feature of the alveoli increases the rate of diffusion of gases into and out of the blood by providing a short diffusion distance?

   [1 mark]

   • Aa large surface area
   • Bthin walls
   • Ca good blood supply
   • Dgood ventilation with air

   (b)

   Why do the alveoli have such a large total surface area for gas exchange?

   [1 mark]

   • Athere are millions of individual alveoli, each contributing its own surface area
   • Bthey contain no cartilage
   • Cthey are lined with mucus
   • Dthey are surrounded by ribs

   (c)

   Explain why a good blood supply to the alveoli is important for efficient gas exchange.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student measured the percentage of oxygen, carbon dioxide and water vapour in air samples breathed in and breathed out by a volunteer, using gas sensors connected to a data logger.

   (a)

   Compared with inspired air, expired air contains:

   [1 mark]

   • Amore oxygen and less carbon dioxide
   • Bthe same amount of oxygen and carbon dioxide
   • Cless oxygen and more carbon dioxide
   • Dless oxygen and less carbon dioxide

   (b)

   Which gas, in addition to carbon dioxide, has a higher percentage in expired air than in inspired air?

   [1 mark]

   • Anitrogen
   • Bhelium
   • Chydrogen
   • Dwater vapour

   (c)

   Explain why expired air contains less oxygen than inspired air.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A doctor explained to a patient with a persistent cough that smoking had damaged the cilia lining their trachea and bronchi, reducing their ability to clear mucus and trapped particles from the airways.

   (a)

   Explain the normal roles of goblet cells, mucus and ciliated cells in protecting the breathing system, and explain why damage to the cilia, as in this patient, increases the risk of chest infections.

   [3 marks]

   (b)

   State the function of cartilage in the trachea, and explain why the alternating contraction of the internal and external intercostal muscles, together with the diaphragm, is needed to move air into and out of the lungs.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A sports scientist monitored a volunteer's rate and depth of breathing, and the oxygen and carbon dioxide content of their blood, before, during and immediately after a period of vigorous exercise on a treadmill.

   (a)

   Explain, in terms of the intercostal muscles and diaphragm, why both the rate and depth of breathing increase during vigorous exercise.

   [6 marks]

   (b)

   Explain why increasing both the rate and depth of breathing during exercise helps to maintain the concentration gradients needed for efficient gas exchange at the alveoli, and explain what would happen to a person's blood oxygen and carbon dioxide levels if their breathing rate could not increase during exercise.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A physiotherapist measured a patient's chest circumference at the top of a breath in and at the end of a breath out, and noted that their ribs moved outward and upward during inhalation and returned to their resting position during exhalation.

   (a)

   What happens to the volume of the thorax during inhalation, as the ribs move upward and outward?

   [1 mark]

   • Ait decreases
   • Bit stays the same
   • Cit increases
   • Dit becomes negative

   (b)

   As the volume of the thorax increases during inhalation, what happens to the air pressure inside the lungs relative to the air pressure outside the body?

   [1 mark]

   • Ait becomes higher than the pressure outside
   • Bit becomes lower than the pressure outside
   • Cit stays exactly equal to the pressure outside
   • Dit is not affected by the change in thorax volume

   (c)

   Explain why air flows into the lungs when the pressure inside the lungs becomes lower than the pressure of the air outside the body.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   During an asthma attack, the smooth muscle in a patient's bronchioles contracted, narrowing the airways and making it harder for air to reach the alveoli, so the patient's rate and depth of breathing both increased in an effort to maintain their oxygen supply.

   (a)

   Which structures does air pass through, in the correct order, on its way from the trachea to the alveoli?

   [1 mark]

   • Abronchi then bronchioles
   • Bbronchioles then bronchi
   • Calveoli then bronchi
   • Dbronchi then larynx

   (b)

   Why does cartilage in the trachea help maintain airflow, even though this patient's bronchioles have narrowed instead?

   [1 mark]

   • Acartilage contracts to narrow the trachea
   • Bcartilage produces mucus
   • Ccartilage removes carbon dioxide from the air
   • Dcartilage rings keep the trachea open, preventing it from collapsing, so air always has a clear pathway into the airways below

   (c)

   Explain why narrowed bronchioles, as in this patient's asthma attack, would reduce the rate at which oxygen can reach the alveoli and diffuse into the blood.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A construction worker who had inhaled large amounts of fine dust over many years developed scarring and thickening of the walls of some of their alveoli, along with a persistently raised breathing rate even at rest.

   (a)

   Explain how thickened, scarred alveoli walls would reduce the rate of gas exchange in this worker's lungs.

   [3 marks]

   (b)

   Explain why this reduction in gas exchange would result in the worker having a persistently raised breathing rate, even while resting.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A group of mountaineers climbed to a high altitude, where the concentration of oxygen in the air is much lower than at sea level; several of the climbers noticed that both their breathing rate and depth increased substantially soon after arriving at altitude, even while resting.

   (a)

   Explain, in terms of gas exchange at the alveoli, why breathing air with a lower oxygen concentration at altitude makes it harder for the climbers' blood to become as fully oxygenated as it would be at sea level.

   [6 marks]

   (b)

   Explain why increasing both the rate and depth of breathing at altitude, as observed in these climbers, would help to increase the amount of oxygen entering their blood, and suggest one further way in which the climbers' bodies might respond over time to a lower oxygen concentration to further improve oxygen delivery to the tissues.

   [6 marks]

   Total for question 8: 12 marks

End of questions