Cambridge IGCSE Biology
Cambridge IGCSE Biology 11 Gas Exchange in Humans Exam Questions
Free Cambridge IGCSE Biology revision for 11 Gas Exchange in Humans: what you need to know, common mistakes and exam-style questions with answers. Covers the breathing system, features of gas exchange surfaces, inspired and expired air, the effect of exercise on breathing and the mechanism of ventilation.
Practise 11 Gas Exchange in Humans with past papers
Once you have learnt this topic, find the 11 Gas Exchange in Humans questions in real Cambridge IGCSE Biology past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
StemUp mark scheme flashcards
GCSE Biology Triple Science Flashcards for 2027 Onwards
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Then test yourself with the questions on this page.
From £7.99View flashcards
About Cambridge IGCSE Biology 11 Gas Exchange in Humans
Gas exchange in humans covers the structure of the breathing system and how oxygen and carbon dioxide move across the alveoli in Cambridge IGCSE Biology. Core candidates identify the larynx, trachea, bronchi, bronchioles, alveoli, ribs, intercostal muscles and diaphragm, list the features of gas exchange surfaces, compare inspired and expired air, and investigate the effect of exercise on breathing. Extended candidates explain the role of the intercostal muscles and diaphragm in ventilation, how goblet cells and ciliated cells protect the airways, and why breathing rate and depth stay raised after exercise. Pressure and volume changes are a common source of lost marks.
What you need to know
- Breathing system Air passes through the larynx, trachea, bronchi and bronchioles to the alveoli. Cartilage rings keep the trachea open. The ribs, internal and external intercostal muscles and diaphragm move the thorax.
- Gas exchange surfaces Alveoli have a large surface area, a thin surface (short diffusion distance), a good blood supply and good ventilation with air, which together maintain steep concentration gradients.
- Inspired and expired air Expired air contains less oxygen, more carbon dioxide and more water vapour than inspired air, and is warmer. Limewater turns milky (cloudy) faster with expired air because it contains more carbon dioxide.
- Exercise Physical activity increases the rate and depth of breathing. Investigate by counting breaths per minute before and after exercise. Extended: carbon dioxide concentration in the blood rises, detected by the brain, which increases breathing rate and depth.
- Ventilation (Extended) Breathing in: external intercostal muscles contract, ribs move up and out, diaphragm contracts and flattens, thorax volume increases, pressure decreases and air moves in. Breathing out is the reverse; internal intercostal muscles contract in forced exhalation.
- Protection of the airways (Extended) Goblet cells produce mucus that traps pathogens and particles. Ciliated cells beat to move mucus up and away from the lungs to the throat.
Common mistakes in 11 Gas Exchange in Humans
- Saying air rushes in, which makes the chest expand. The thorax volume increases first, lowering pressure, and air then moves in.
- Saying expired air contains no oxygen. It still contains about 16% oxygen.
- Saying the diaphragm moves up when it contracts. It contracts and flattens (moves down).
- Saying cilia trap dust. Mucus traps particles; cilia move the mucus.
- Saying we breathe in oxygen and breathe out carbon dioxide only. Both inspired and expired air are mostly nitrogen and contain both gases.
Try three 11 Gas Exchange in Humans exam-style questions
1. State two features of the alveoli that make them efficient gas exchange surfaces. (2 marks)
Show the mark scheme answer
Large surface area; thin walls (short diffusion distance); good blood supply; good ventilation; any two.
2. Describe the changes in the thorax that cause air to be breathed in. (4 marks)
Show the mark scheme answer
External intercostal muscles contract and ribs move up and out; diaphragm contracts and flattens; volume of thorax increases; pressure inside decreases below atmospheric pressure so air moves in.
3. A student's breathing rate was 14 breaths per minute at rest and 35 breaths per minute after exercise. Calculate the percentage increase. (2 marks)
Show the mark scheme answer
(35 - 14) / 14 x 100; = 150%.
11 Gas Exchange in Humans FAQs
What does Cambridge IGCSE Biology 11 Gas Exchange in Humans cover?
It covers the structure of the breathing system, the features of gas exchange surfaces, differences between inspired and expired air, the effects of exercise and, for Extended candidates, the mechanism of ventilation.
Which paper is 11 Gas Exchange in Humans examined in?
It is examined in the theory and multiple choice papers: Papers 1 and 3 for Core candidates, or Papers 2 and 4 for Extended candidates. Practical skills linked to it can also appear in Paper 5 (Practical Test) or Paper 6 (Alternative to Practical).
What do I need to compare in inspired and expired air?
Learn that expired air has less oxygen, more carbon dioxide, more water vapour and a higher temperature, and know the limewater experiment that shows the difference in carbon dioxide.
