IGCSE Biology Topic 11: Gas Exchange in Humans MCQs – 30 Practice Questions with Answers (Cambridge 0610)
Free practice for Cambridge IGCSE Biology 0610 on gas exchange in humans, covering the breathing system, alveoli, ventilation, inspired and expired air, and the link with physical activity, with every question followed by a worked explanation.
The breathing system and gas exchange surfaces
Q1. Which combination describes the features of a good gas exchange surface in humans?
- (A) Small surface area, thick surface, poor blood supply, still air
- (B) Large surface area, thick surface, good blood supply, good ventilation with air
- (C) Large surface area, thin surface, good blood supply, good ventilation with air
- (D) Large surface area, thin surface, poor blood supply, still air
Show Answer
Answer: C – Gas exchange surfaces have a large area, a thin surface, a good blood supply and good ventilation with air.
Q2. In which order does inhaled air pass through the breathing system to reach the alveoli?
- (A) Trachea → bronchi → bronchioles → alveoli
- (B) Bronchi → trachea → alveoli → bronchioles
- (C) Alveoli → bronchioles → bronchi → trachea
- (D) Trachea → bronchioles → bronchi → alveoli
Show Answer
Answer: A – Air travels down the trachea, into the bronchi, through the bronchioles and finally to the alveoli.
Q3. What is the function of the cartilage in the trachea?
- (A) It traps pathogens in mucus
- (B) It sweeps mucus and trapped particles away from the lungs
- (C) It absorbs oxygen into the blood
- (D) It holds the trachea open so air can pass freely
Show Answer
Answer: D – Rings of cartilage support the trachea and keep the airway open.
Q4. At the alveoli and their associated capillaries, in which directions do oxygen and carbon dioxide move?
- (A) Oxygen moves out of the blood and carbon dioxide moves into the blood
- (B) Oxygen moves into the blood and carbon dioxide moves out of the blood
- (C) Both gases move into the blood together
- (D) Both gases move out of the blood together
Show Answer
Answer: B – Oxygen diffuses from the alveoli into the blood while carbon dioxide diffuses from the blood into the alveoli.
Q5. Why does a thin alveolar surface help gas exchange?
- (A) It gives a short diffusion distance, so gases cross quickly
- (B) It prevents any water vapour leaving the lungs
- (C) It stops blood reaching the alveoli
- (D) It increases the volume of air that can be held in each lung at one time
Show Answer
Answer: A – A thin surface shortens the distance gases must diffuse, speeding up exchange.
Q6. Why does a good blood supply help gas exchange at the alveoli?
- (A) It thickens the alveolar walls for protection
- (B) It warms the air before it reaches the alveoli so that diffusion happens faster
- (C) It constantly replaces blood, maintaining the concentration gradients
- (D) It filters carbon dioxide out of inhaled air
Show Answer
Answer: C – Flowing blood carries oxygen away and brings carbon dioxide in, keeping the gradients steep for diffusion.
Q7. Why does a large surface area help gas exchange in the lungs?
- (A) It lets the lungs store more carbon dioxide
- (B) It provides more area over which diffusion can happen at once
- (C) It reduces the number of capillaries needed
- (D) It slows down the movement of air through the lungs so gases have more time
Show Answer
Answer: B – Millions of alveoli together give a very large area, so much more gas can diffuse at the same time.
Q8. Why is good ventilation with air important for gas exchange?
- (A) It dries out the alveolar surface completely
- (B) It stops carbon dioxide diffusing out of the blood and into the alveoli during breathing
- (C) It pushes blood through the lung capillaries
- (D) It refreshes the air in the alveoli, maintaining the concentration gradients
Show Answer
Answer: D – Fresh air brings in oxygen and removes carbon dioxide, keeping diffusion gradients in the right direction.
Q9. Which structures carry air from the trachea into each lung?
- (A) The larynx
- (B) The diaphragm
- (C) The bronchi
- (D) The ribs
Show Answer
Answer: C – The trachea divides into two bronchi, one entering each lung.
Q10. Where in the breathing system does gas exchange with the blood actually take place?
- (A) In the alveoli
- (B) In the bronchi
- (C) In the larynx
- (D) In the trachea
Show Answer
Answer: A – Gas exchange happens across the thin walls of the alveoli into their associated capillaries.
Ventilation: ribs, intercostal muscles and diaphragm
Q11. During breathing in, what do the external intercostal muscles do?
- (A) They relax so the ribs move down and in
- (B) They contract so the ribs move up and out
- (C) They contract so the diaphragm domes upwards
- (D) They relax so the diaphragm flattens
Show Answer
Answer: B – Contraction of the external intercostal muscles raises the ribs and moves them outwards.
Q12. During breathing in, what happens to the diaphragm?
- (A) It relaxes and domes upwards
- (B) It relaxes and stays flat
- (C) It contracts and domes upwards
- (D) It contracts and flattens
Show Answer
Answer: D – The diaphragm contracts and flattens during inspiration, increasing the volume of the thorax.
Q13. What happens to the volume and pressure in the thorax during breathing in?
- (A) Volume increases and pressure falls
- (B) Volume decreases and pressure rises
- (C) Volume increases and pressure rises
- (D) Volume decreases and pressure falls
Show Answer
Answer: A – The ribs and diaphragm increase thorax volume, which lowers the air pressure inside the lungs.
Q14. Why does air flow into the lungs during breathing in?
- (A) The pressure inside the lungs rises above atmospheric pressure
- (B) The pressure outside the body falls to zero
- (C) The pressure inside the lungs falls below atmospheric pressure
- (D) The alveoli actively suck air in by contracting
Show Answer
Answer: C – Air flows down a pressure gradient, from higher pressure outside to lower pressure inside the lungs.
Q15. During quiet breathing out, what happens to the muscles of breathing?
- (A) The diaphragm contracts and the external intercostals contract
- (B) The diaphragm and external intercostal muscles relax
- (C) The internal intercostal muscles contract strongly
- (D) The diaphragm contracts while the ribs move down
Show Answer
Answer: B – In quiet expiration the diaphragm relaxes and domes up, the ribs move down and in, and thorax volume falls.
Q16. When are the internal intercostal muscles mainly used?
- (A) During quiet breathing in
- (B) During sleep when breathing is shallow and the diaphragm is relaxed
- (C) When the diaphragm is fully relaxed
- (D) During forced breathing out, pulling the ribs down and in
Show Answer
Answer: D – The internal intercostal muscles contract during forced expiration, moving the ribs down and in.
Q17. What is the role of the ribs in ventilation?
- (A) They move to change the volume of the thorax, driving pressure changes
- (B) They produce mucus in their lining to trap dust particles before they reach the lungs
- (C) They carry blood to the alveoli
- (D) They contract to flatten the diaphragm
Show Answer
Answer: A – Rib movements, driven by the intercostal muscles, change thorax volume and so change lung pressure.
Q18. What happens to the pressure inside the lungs during breathing out?
- (A) It falls below atmospheric pressure and stays there until the next breath in
- (B) It becomes equal to the pressure in the blood
- (C) It rises above atmospheric pressure, pushing air out
- (D) It drops to zero as the lungs empty
Show Answer
Answer: C – As thorax volume falls, lung pressure rises above atmospheric pressure and air flows out.
Q19. How do the diaphragm and intercostal muscles work together in ventilation?
- (A) Only one of them acts during any single breath
- (B) Both act to change thorax volume and therefore lung pressure
- (C) The diaphragm changes pressure while the ribs block air flow
- (D) The intercostals move air while the diaphragm moves blood
Show Answer
Answer: B – The diaphragm and the intercostal muscles together produce the volume and pressure changes that ventilate the lungs.
Q20. During vigorous exercise, breathing out becomes more active. Which muscles contract to force air out?
- (A) The external intercostal muscles only
- (B) The diaphragm only
- (C) The muscles of the larynx only
- (D) The internal intercostal muscles
Show Answer
Answer: D – Forced expiration uses the internal intercostal muscles to pull the ribs down and in quickly.
Inspired and expired air, protection and exercise
Q21. Compared with expired air, inspired air contains which amounts of oxygen and carbon dioxide?
- (A) Less oxygen and more carbon dioxide
- (B) The same amounts of both gases
- (C) More oxygen and less carbon dioxide
- (D) Less oxygen and less carbon dioxide
Show Answer
Answer: C – Inspired air is richer in oxygen and poorer in carbon dioxide than expired air.
Q22. A pupil bubbles inspired air through limewater, then bubbles expired air through a fresh sample. What is the expected result?
- (A) The expired-air sample turns milky faster, showing it contains more carbon dioxide
- (B) The inspired-air sample turns milky faster, showing it contains more carbon dioxide
- (C) Both samples turn milky at exactly the same rate
- (D) Neither sample changes, because air contains no carbon dioxide
Show Answer
Answer: A – Limewater turns milky in the presence of carbon dioxide, and expired air contains more of it than inspired air.
Q23. Apart from its gas composition, how does expired air differ from inspired air?
- (A) It is colder and drier
- (B) It is warmer and contains more water vapour
- (C) It is colder and contains less water vapour
- (D) It is warmer but contains less water vapour
Show Answer
Answer: B – Expired air has been warmed in the body and picks up water vapour from the moist airways.
Q24. What does limewater test for in the investigation of inspired and expired air?
- (A) Oxygen
- (B) Nitrogen
- (C) Water vapour from the moist lining of the airways
- (D) Carbon dioxide
Show Answer
Answer: D – Limewater is used as a test for carbon dioxide, turning milky when carbon dioxide is present.
Q25. Why does expired air still contain a large amount of oxygen?
- (A) Not all of the oxygen in inspired air is removed during one breath
- (B) The lungs manufacture extra oxygen during breathing out
- (C) Carbon dioxide is converted back into oxygen in the alveoli during breathing out
- (D) Blood releases its oxygen into the alveoli on breathing out
Show Answer
Answer: A – Only part of the inspired oxygen diffuses into the blood, so much of it remains in expired air.
Q26. Which cells in the lining of the airways produce mucus?
- (A) Ciliated cells
- (B) Muscle cells
- (C) Goblet cells
- (D) Cartilage cells
Show Answer
Answer: C – Goblet cells secrete mucus that lines the airways.
Q27. What is the protective role of mucus in the breathing system?
- (A) It kills pathogens with acid
- (B) It traps pathogens and particles before they reach the lungs
- (C) It absorbs oxygen from inhaled air for the blood as air passes over the lining
- (D) It holds the trachea open
Show Answer
Answer: B – Mucus traps inhaled pathogens and particles so they do not reach the delicate alveoli.
Q28. What do ciliated cells do in the breathing system?
- (A) They beat to move mucus, with its trapped particles, out of the airways
- (B) They produce mucus to line the airways
- (C) They absorb carbon dioxide from the blood and pass it into the airways for removal
- (D) They form rings that hold the trachea open
Show Answer
Answer: A – Ciliated cells beat in waves that move mucus and its trapped pathogens and particles away from the lungs.
Q29. During physical activity, why do the rate and depth of breathing increase?
- (A) The lungs run out of air completely
- (B) Oxygen in the blood rises and stops the brain signalling completely for faster breathing
- (C) Muscles stop producing carbon dioxide
- (D) Carbon dioxide concentration in the blood rises, which is detected by the brain
Show Answer
Answer: D – Increased carbon dioxide in the blood is detected by the brain, which raises the rate and depth of breathing.
Q30. After a pupil stops exercising, breathing stays fast and deep for a while. What best explains this?
- (A) The diaphragm stays permanently flattened after exercise and never returns to its domed shape
- (B) The brain keeps responding until blood carbon dioxide falls back towards normal
- (C) The ribs can no longer move down and in
- (D) The alveoli stop exchanging gases once exercise ends
Show Answer
Answer: B – Breathing returns to normal only as the raised blood carbon dioxide level falls, so the brain’s signal fades gradually.
Revise any questions you missed, especially how rib and diaphragm movements change thorax pressure, then retest yourself on inspired and expired air.