About Gas exchange in A Level Biology
Gas exchange is one of the 11 main topics in our A Level Biology (Cambridge (CAIE) 9700) question bank, and about 4% of its real questions come from it. Tayyari Karo has 28 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2; 24 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 20 medium, 4 hard, 4 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 6 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
May/June 2026 · Paper 1 · Gas exchange
Gas exchange between air in the alveoli and blood in the capillaries is dependent on the process of diffusion. The rate of diffusion is proportional to (surface area × concentration difference) ÷ distance over which diffusion occurs. What would result in the fastest rate of diffusion?
- The distance is doubled, and the surface area is doubled.
- The concentration difference is halved, and the surface area is doubled.
- The distance is halved, and the surface area is doubled.
- The concentration difference is trebled, and the other variables are kept the same.
Show answer and explanation
Answer: C. The distance is halved, and the surface area is doubled.
Halving distance and doubling area gives a four-fold increase, larger than the other options.
May/June 2025 · Paper 1 · Gas exchange
Asthma can affect children and adults. The air passages become narrower, severely restricting the flow of air into the lungs. Salbutamol is a drug that widens the air passages to relieve the symptoms of asthma. How does salbutamol relieve the symptoms of asthma?
- It decreases mucus secretions in the terminal bronchioles.
- It decreases the surface area of the alveoli.
- It causes recoil of elastic tissue in the bronchioles.
- It relaxes smooth muscle in the bronchi and bronchioles.
Show answer and explanation
Answer: D. It relaxes smooth muscle in the bronchi and bronchioles.
Salbutamol is a bronchodilator that relaxes the smooth muscle in the walls of the bronchi and bronchioles, widening the airways.
May/June 2024 · Paper 1 · Gas exchange
Which tissues are present in a bronchus?
| cartilage | ciliated epithelium | smooth muscle
A | ✓ | ✓ | ✓
B | ✓ | ✓ | ✗
C | ✓ | ✗ | ✓
D | ✗ | ✓ | ✓
- cartilage ✓, ciliated epithelium ✓, smooth muscle ✓
- cartilage ✓, ciliated epithelium ✓, smooth muscle ✗
- cartilage ✓, ciliated epithelium ✗, smooth muscle ✓
- cartilage ✗, ciliated epithelium ✓, smooth muscle ✓
Show answer and explanation
Answer: A. cartilage ✓, ciliated epithelium ✓, smooth muscle ✓
A bronchus wall contains cartilage rings for support, ciliated epithelium to move mucus, and smooth muscle to control airway diameter — all three are present.
October/November 2024 · Paper 1 · Gas exchange
Which tissues are present in the walls of a trachea and an alveolus, for epithelium with goblet cells and for smooth muscle?
- trachea: epithelium with goblet cells present, smooth muscle present; alveolus: both not present
- trachea: epithelium with goblet cells present, smooth muscle present; alveolus: epithelium not present, smooth muscle present
- trachea: epithelium with goblet cells present, smooth muscle not present; alveolus: both present
- trachea: both not present; alveolus: epithelium not present, smooth muscle present
Show answer and explanation
Answer: A. trachea: epithelium with goblet cells present, smooth muscle present; alveolus: both not present
The trachea wall contains ciliated epithelium with goblet cells and smooth muscle; the alveolus wall is a thin squamous epithelium with no goblet cells and no smooth muscle.
May/June 2023 · Paper 1 · Gas exchange
Which statements about all bronchioles are correct? 1 They have epithelium. 2 They have goblet cells. 3 They have muscle tissue.
- 1, 2 and 3
- 1 and 3 only
- 2 only
- 3 only
Show answer and explanation
Answer: B. 1 and 3 only
All bronchioles are lined with epithelium and have smooth muscle in their walls (allowing constriction/dilation); however, the smallest (terminal) bronchioles lack goblet cells, so goblet cells are not present in all bronchioles.
May/June 2022 · Paper 1 · Gas exchange
Which statement explains the importance of the chloride shift in red blood cells (RBC)?
- Carbon dioxide diffuses from blood plasma into RBC and chloride ions diffuse out of RBC to maintain a balance of positive and negative ions.
- Hydrogencarbonate ions diffuse into plasma from RBC and chloride ions diffuse into RBC to maintain a balance of positive and negative ions.
- Carbon dioxide in RBC together with chloride ions stimulate the release of oxygen from haemoglobin to allow increased levels of respiration.
- Hydrogencarbonate ions diffuse into RBC from plasma and chloride ions diffuse into plasma to maintain a balance of positive and negative ions.
Show answer and explanation
Answer: B. Hydrogencarbonate ions diffuse into plasma from RBC and chloride ions diffuse into RBC to maintain a balance of positive and negative ions.
As hydrogencarbonate ions (formed inside the RBC from CO2 + water) diffuse out into the plasma, chloride ions diffuse into the RBC to replace the lost negative charge and maintain electrochemical balance.
