IGCSE · Practice questions · The breathing system

Large, thin, supplied and ventilated.

Six original Cambridge-style questions on the structure of the breathing system, the features of the alveoli as a gas exchange surface and how the airways are protected.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Four features, one job.

Airway order: larynx, trachea, bronchi, bronchioles, alveoli.
Gas exchange surface: large surface area, thin surface, good blood supply, good ventilation with air.
Say why: area = more crossing at once; thin = short distance; blood and ventilation = steep concentration gradients.
Extended: cartilage holds the trachea open; goblet cells make mucus; mucus traps; cilia sweep.

Recall

[4 marks]

Starting from the larynx, name in order the structures that air passes through to reach the blood in the lungs.

Trachea. ✓
Bronchus (bronchi). ✓
Bronchioles. ✓
Alveoli, then across the alveolus wall and capillary wall into the blood. ✓

Explain

[4 marks]

Describe four features of the alveoli that make them an efficient gas exchange surface, and explain how each one helps.

Large surface area (millions of alveoli), so more oxygen and carbon dioxide can diffuse at the same time. ✓
Thin surface (walls one cell thick), so the diffusion distance is short. ✓
Good blood supply (dense capillaries), which carries oxygen away and brings carbon dioxide, keeping the concentration gradients steep. ✓
Good ventilation with air, which brings fresh air and removes carbon dioxide, keeping the gradients steep. ✓

Data

[3 marks]

In a model of an alveolus, the rate of oxygen uptake with all four features was 10 units per second. The table shows the rate with one feature removed.

Feature removed	Rate / units per second
large surface area	2.0
thin surface	3.0
good blood supply	3.0
good ventilation	3.5

(a) Calculate the rate without a large surface area as a percentage of the full rate. (b) Explain why removing the blood supply reduces the rate.

(a) 2.0 ÷ 10 × 100 = 20%. ✓
(b) Without flowing blood, oxygen is not carried away from the capillary, so its concentration in the blood rises. ✓
The concentration gradient between the air in the alveolus and the blood becomes smaller, so less oxygen diffuses in. ✓

Explain

[2 marks]

The disease emphysema breaks down the walls between alveoli, forming fewer, larger air spaces. Suggest why people with emphysema become breathless.

Fewer, larger air spaces have a much smaller total surface area for gas exchange. ✓
So less oxygen diffuses into the blood per minute, and the person must breathe faster to get enough oxygen. ✓

Recall

[3 marks]

Extended. State the function of the cartilage in the trachea, and state where the internal and external intercostal muscles are found.

Cartilage (in C-shaped rings) supports the trachea and keeps it open, so it does not collapse when the pressure inside falls. ✓
The external intercostal muscles lie between the ribs on the outer side. ✓
The internal intercostal muscles lie between the ribs on the inner side. ✓

Explain

[4 marks]

Extended. Explain how goblet cells, mucus and ciliated cells protect the breathing system from pathogens and particles. Suggest why smokers, whose cilia are damaged, cough more and get more chest infections.

Goblet cells secrete mucus onto the lining of the airways. ✓
The sticky mucus traps dust, particles and pathogens such as bacteria. ✓
Cilia on ciliated cells beat to sweep the mucus up to the throat, where it is swallowed, so pathogens do not reach the alveoli. ✓
With damaged cilia the mucus collects in the airways; coughing is the only way to move it, and trapped pathogens stay in the lungs and can cause infections. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.