A-Level Biology Topic 9: Gas Exchange MCQs – 30 Practice Questions with Answers (Cambridge 9700)
Free practice for Cambridge A-Level Biology 9700 on the human gas exchange system, with every question followed by a short worked explanation to help you check your understanding.
Structure of the Gas Exchange System
Q1. What is the main function of the human gas exchange system?
- (A) To remove urea from the blood
- (B) To take oxygen into the blood and remove carbon dioxide
- (C) To digest food into small molecules in a typical human cell
- (D) To pump blood around the body
Show Answer
Answer: B – The system takes oxygen into the blood and excretes carbon dioxide from the blood.
Q2. Which sequence shows the correct route taken by inhaled air?
- (A) Alveoli, bronchioles, bronchi, trachea
- (B) Trachea, alveoli, bronchi, bronchioles
- (C) Bronchi, trachea, bronchioles, alveoli
- (D) Trachea, bronchi, bronchioles, alveoli
Show Answer
Answer: D – Air passes down the trachea, into the bronchi, then the smaller bronchioles, and finally reaches the alveoli.
Q3. What keeps the trachea open during breathing?
- (A) Rings of cartilage in its wall
- (B) A layer of squamous epithelium
- (C) Bands of elastic fibres only
- (D) The capillary network around it
Show Answer
Answer: A – Rings of cartilage support the trachea and prevent it from collapsing when air pressure changes.
Q4. How do bronchioles differ from the trachea and bronchi?
- (A) They contain more cartilage than the trachea
- (B) They are lined with squamous epithelium throughout
- (C) They lack cartilage but contain smooth muscle
- (D) They have no epithelium in their walls
Show Answer
Answer: C – Cartilage becomes less common further down the airways and is absent in bronchioles, where smooth muscle is present.
Q5. What surrounds each alveolus?
- (A) A ring of cartilage
- (B) A dense network of capillaries
- (C) A layer of goblet cells
- (D) A sheet of smooth muscle under the conditions described
Show Answer
Answer: B – Every alveolus is wrapped in a capillary network, so blood is brought very close to the air in the alveolus.
Q6. What is the wall of an alveolus made from?
- (A) A single layer of squamous epithelium
- (B) Several layers of ciliated epithelium
- (C) A thick layer of cartilage and muscle
- (D) A single layer of goblet cells
Show Answer
Answer: A – The alveolar wall is one cell thick, made of squamous epithelium, which keeps the diffusion distance very short.
Q7. What is the main product of goblet cells in the gas exchange system?
- (A) Digestive enzymes
- (B) Hormones for breathing control
- (C) Elastic fibres for recoil
- (D) Mucus that traps particles
Show Answer
Answer: D – Goblet cells secrete mucus, which traps dust, bacteria and other particles from inhaled air.
Q8. What is the function of ciliated epithelial cells in the airways?
- (A) To absorb oxygen into the blood
- (B) To secrete cartilage into the airway wall under normal conditions
- (C) To sweep mucus upwards, away from the lungs
- (D) To contract and narrow the airways
Show Answer
Answer: C – The cilia beat in a coordinated way to move mucus, with its trapped particles, up towards the throat.
Q9. What do mucous glands in the airway walls contribute to lung health?
- (A) Mucus that traps inhaled particles and pathogens
- (B) Cartilage that holds the bronchi open
- (C) Blood capillaries for gas exchange
- (D) Elastic fibres that stretch the alveoli in a typical human cell
Show Answer
Answer: A – Mucous glands add mucus to the airway lining, helping to trap particles before they reach the delicate alveoli.
Q10. What does smooth muscle in the walls of bronchioles control?
- (A) The production of mucus by goblet cells
- (B) The beating of cilia on epithelial cells
- (C) The thickness of the alveolar wall
- (D) The diameter of the airways
Show Answer
Answer: D – Contraction or relaxation of smooth muscle narrows or widens the bronchioles, changing airflow to different lung regions.
Keeping the Airways Clean and Open
Q11. What is the main function of cartilage in the gas exchange system?
- (A) To secrete mucus into the airways
- (B) To support the airways and keep them open
- (C) To carry oxygen to respiring tissues in the system described
- (D) To sweep particles out of the lungs
Show Answer
Answer: B – Cartilage provides rigid support so the trachea and bronchi stay open as air moves in and out.
Q12. What is the role of elastic fibres in the walls of alveoli?
- (A) To produce mucus for trapping dust
- (B) To contract and close the alveoli
- (C) To let alveoli stretch and then recoil
- (D) To form a barrier against pathogens for the organism involved
Show Answer
Answer: C – Elastic fibres allow alveoli to stretch as they fill with air and recoil as air is breathed out.
Q13. Why is squamous epithelium well suited to the alveolar wall?
- (A) Its thin, flat cells give a short diffusion distance
- (B) Its cilia sweep mucus out of the alveoli
- (C) Its thick cells protect against damage
- (D) Its goblet cells secrete large volumes of mucus under the conditions described
Show Answer
Answer: A – Flat, thin squamous cells mean gases only have to diffuse across a very short distance into the blood.
Q14. Why is the capillary network around alveoli an advantage for gas exchange?
- (A) It produces mucus to line the alveoli
- (B) It keeps the alveoli permanently inflated
- (C) It supplies cartilage to the alveolar wall in most ordinary conditions
- (D) It maintains a steep diffusion gradient for gases
Show Answer
Answer: D – Flowing blood constantly brings blood low in oxygen to the alveoli and carries oxygenated blood away, maintaining the gradient.
Q15. If the cilia lining the airways are damaged, what is the most likely result?
- (A) The alveoli become thicker and stronger during the process described
- (B) Mucus builds up and infection becomes more likely
- (C) Cartilage grows into the bronchioles
- (D) Oxygen diffuses more rapidly into blood
Show Answer
Answer: B – Without working cilia, mucus is not cleared, so trapped pathogens remain in the airways and infection risk rises.
Q16. In which direction does oxygen diffuse at the alveoli?
- (A) From blood in capillaries into the alveoli
- (B) From alveolar cells into the cartilage
- (C) From air in the alveoli into the blood
- (D) From bronchioles directly into the trachea
Show Answer
Answer: C – Oxygen moves down its diffusion gradient from the air in the alveoli into the blood in the capillaries.
Q17. In which direction does carbon dioxide diffuse at the alveoli?
- (A) From blood in the capillaries into the alveoli
- (B) From air in the alveoli into the cartilage in a typical human cell
- (C) From the trachea into the bronchioles
- (D) From goblet cells into the mucus layer
Show Answer
Answer: A – Carbon dioxide moves down its gradient from the blood, where its concentration is higher, into the alveolar air.
Q18. Which combination of features makes alveoli efficient for gas exchange?
- (A) Thick walls, small area and dry surfaces
- (B) Thick walls, rich blood supply and dry surfaces during normal activity
- (C) Thin walls, small area and slow blood flow
- (D) Large surface area, thin walls and a rich blood supply
Show Answer
Answer: D – A large area, thin walls and a good blood supply together give fast diffusion of gases in both directions.
Q19. A plan diagram of a transverse section through the trachea wall would show which combination?
- (A) Alveoli, squamous epithelium and capillaries only
- (B) Cartilage, ciliated epithelium and goblet cells
- (C) Smooth muscle, alveoli and elastic fibres only
- (D) Goblet cells, alveoli and cartilage rings only
Show Answer
Answer: B – The trachea wall contains cartilage for support, ciliated epithelium for clearance, and goblet cells that secrete mucus.
Q20. How does a bronchus differ from a bronchiole?
- (A) A bronchus is narrower and has more smooth muscle for the organism involved
- (B) A bronchus has no epithelium in its wall
- (C) A bronchus is wider and contains cartilage in its wall
- (D) A bronchus is surrounded by alveoli directly
Show Answer
Answer: C – Bronchi are wider airways than bronchioles and still contain cartilage, which bronchioles lack.
Gas Exchange in the Alveoli
Q21. During vigorous exercise, how does gas exchange at the alveoli change?
- (A) Less air is moved in and out of the lungs under the conditions described
- (B) Blood flow to the lungs falls sharply
- (C) Diffusion gradients become smaller
- (D) More air and blood reach the alveoli, so exchange rises
Show Answer
Answer: D – Faster, deeper breathing and increased blood flow bring more oxygen to the alveoli and remove carbon dioxide faster.
Q22. Which cells in the airway epithelium itself secrete mucus?
- (A) Goblet cells
- (B) Squamous epithelial cells
- (C) Smooth muscle cells
- (D) Cartilage cells
Show Answer
Answer: A – Goblet cells are found among the ciliated epithelial cells and secrete mucus onto the airway surface.
Q23. What happens when smooth muscle in bronchiole walls contracts?
- (A) The airways widen and airflow increases during the process described
- (B) The airways narrow and airflow is reduced
- (C) The alveoli fill with mucus
- (D) The cartilage in the trachea dissolves
Show Answer
Answer: B – Contraction of the smooth muscle reduces the diameter of the bronchioles, restricting airflow through them.
Q24. Why does the moist surface of the alveoli help gas exchange?
- (A) Water blocks the movement of gases
- (B) Dry surfaces attract more oxygen
- (C) Gases dissolve in the moisture before diffusing
- (D) Moisture thickens the alveolar wall under normal conditions
Show Answer
Answer: C – Oxygen and carbon dioxide dissolve in the thin layer of moisture lining the alveoli, allowing them to diffuse across the wall.
Q25. How does the amount of cartilage change along the airways?
- (A) It decreases, and is absent from bronchioles
- (B) It increases towards the alveoli
- (C) It stays the same in every airway in a typical human cell
- (D) It appears only in the alveoli
Show Answer
Answer: A – Cartilage is plentiful in the trachea, less common in the bronchi, and absent in the bronchioles.
Q26. Where is ciliated epithelium found in the gas exchange system?
- (A) In the walls of the alveoli
- (B) In the walls of the capillaries
- (C) Only on the surface of the lungs
- (D) Lining the trachea and bronchi
Show Answer
Answer: D – Ciliated epithelium lines the trachea and bronchi, where it moves mucus upwards and out of the lungs.
Q27. After blood has passed the alveoli, how has its gas content changed?
- (A) It has gained carbon dioxide and lost oxygen
- (B) It has gained oxygen and lost carbon dioxide
- (C) It has lost both oxygen and carbon dioxide
- (D) Its gas content is unchanged
Show Answer
Answer: B – Blood leaving the alveoli is oxygenated: it has picked up oxygen and given up carbon dioxide.
Q28. Which pair of defences best maintains the health of the gas exchange system?
- (A) Cartilage support and elastic recoil
- (B) Smooth muscle contraction and cartilage rings for the organism involved
- (C) Mucus trapping particles and cilia sweeping them away
- (D) Squamous epithelium and capillary networks
Show Answer
Answer: C – Mucus traps inhaled particles and pathogens, and cilia move the mucus out of the airways.
Q29. Which statement about cartilage in the airways is correct?
- (A) The trachea has cartilage, but bronchioles do not
- (B) Bronchioles have more cartilage than the trachea under the conditions described
- (C) Cartilage is found only in the alveoli
- (D) Cartilage secretes mucus into the airways
Show Answer
Answer: A – Cartilage supports the larger airways and gradually disappears, so bronchioles have none.
Q30. Which summary best explains why alveoli are adapted for gas exchange?
- (A) They have thick walls and a small surface area
- (B) They are dry, rigid and poorly supplied with blood in most ordinary conditions
- (C) They contain cartilage and smooth muscle
- (D) They offer a large, thin, moist surface with a rich blood supply
Show Answer
Answer: D – The combination of large area, thin walls, a moist surface and many capillaries gives rapid diffusion in both directions.
Work through any questions you missed again, then revise those areas before moving on to the next topic.