Gas exchange in the lungs and in leavesAQA A-Level Biology: Subtopic test

1. 1
   Marram grass grows on sand dunes, where water is scarce and winds are strong. Its leaves are rolled, with the stomata on the inner surface, and the inner surface is lined with hairs. A bean plant, which is a typical dicotyledonous plant, grows in moist soil and has flat leaves.

   (a)

   Through which structures does carbon dioxide enter the leaf of the bean plant?

   [1 mark]

   • AThe waxy cuticle
   • BXylem vessels
   • CPhloem sieve tubes
   • DStomata

   (b)

   Which feature of marram grass reduces water loss by transpiration?

   [1 mark]

   • AA thin cuticle to allow rapid gas exchange
   • BStomata on the exposed outer surface of the leaf
   • CRolled leaves with stomata on the inner surface, trapping humid air
   • DA large surface area to volume ratio of the leaf

   (c)

   Explain how the stomata of the bean plant allow the plant to gain carbon dioxide while limiting the loss of water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student dissects the lungs of a sheep to study the gas exchange system, and then uses a model made from a bell jar, a Y-shaped tube and a rubber sheet to show how breathing works. The student also measures the breathing of a volunteer at rest.

   (a)

   What does the student see holding the trachea open in the dissection?

   [1 mark]

   • AC-shaped rings of cartilage
   • BA layer of smooth muscle only
   • CRings of bone
   • DA thick layer of elastic fibres only

   (b)

   The volunteer has a tidal volume of 500 cm³ and breathes 12 times per minute. What is the pulmonary ventilation rate?

   [1 mark]

   • A512 cm³ min⁻¹
   • B6000 cm³ min⁻¹
   • C42 cm³ min⁻¹
   • D600 cm³ min⁻¹

   (c)

   Explain how air enters the lungs during inspiration.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A respiratory clinic treats patients with lung diseases, including pulmonary fibrosis, in which scar tissue thickens the alveolar walls and makes the lungs less elastic. The clinic's researchers also study how smoking affects the risk of lung disease.

   (a)

   A patient with pulmonary fibrosis has a tidal volume of 300 cm³ and breathes 24 times per minute at rest. Calculate the patient's pulmonary ventilation rate and explain why fibrosis reduces the rate of gas exchange.

   [3 marks]

   (b)

   In a study of 50 000 men followed for ten years, the incidence of lung cancer per 100 000 men per year was 14 for men who had never smoked, 90 for those who smoked 1 to 14 cigarettes a day, 170 for those who smoked 15 to 24 a day, and 260 for those who smoked 25 or more a day. Use the data to explain why the study shows a correlation, but not by itself that smoking causes lung cancer, and state what further evidence would support a causal link.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A government is deciding whether to ban smoking in all enclosed public places. It has data from a country that introduced such a ban. Doctors in the same country also treat patients with emphysema, a disease in which the walls of the alveoli break down and the lungs lose elastic tissue.

   (a)

   In the year after the ban, hospital admissions for asthma in children fell by 18%. Over the same year, admissions did not change in a neighbouring country with no ban, and the concentration of airborne particles in bars fell by 90%. Evaluate this evidence that the ban improved lung health, and explain how such evidence can lead to legislation.

   [6 marks]

   (b)

   Explain how the structure of an alveolus allows efficient gas exchange, and why a person with emphysema has a lower rate of gas exchange.

   [6 marks]

   Total for question 4: 12 marks

End of questions