What route does air follow through the breathing system to reach the alveoli?
Larynx → trachea → two bronchi (one into each lung) → smaller bronchioles → alveoli.
Cambridge IGCSE (9–1) Biology 0970 (Extended) (2026–2028) · 11.1
Revise Cambridge IGCSE (9–1) Biology 0970 (Extended) (2026–2028) specification point 11.1, Gas exchange in humans, with free active-recall flashcards. Flip through the set or review every question and answer below.
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What route does air follow through the breathing system to reach the alveoli?
Larynx → trachea → two bronchi (one into each lung) → smaller bronchioles → alveoli.
How are capillaries positioned relative to the alveoli?
Capillaries surround the alveoli, placing blood close to the air in the lungs.
Where are the ribs positioned in the breathing system?
They surround the chest.
Where are the intercostal muscles located?
Between the ribs.
What is the diaphragm?
A sheet of muscle beneath the lungs.
What is the benefit of the alveoli having a large surface area?
Gases can be exchanged between air and blood over a large area.
How does the thin surface of the alveoli help gas exchange?
It gives oxygen and carbon dioxide a short distance to diffuse.
How does a good blood supply around the alveoli support gas exchange?
It carries oxygen away and brings carbon dioxide to the alveoli.
How does good ventilation of the alveoli support gas exchange?
It replaces alveolar air, bringing in oxygen and removing carbon dioxide.
How does expired air differ from inspired air in oxygen, carbon dioxide and water vapour content?
Expired air contains:
Why does expired air contain less oxygen than inspired air?
Oxygen passes from the air in the lungs into the blood.
Why does expired air contain more carbon dioxide than inspired air?
Carbon dioxide passes from the blood into the air in the lungs to be breathed out.
Why does expired air contain more water vapour than inspired air?
Air gains water vapour as it passes through the breathing system.
How can limewater be used to test air for carbon dioxide?
Pass the air through limewater. It turns cloudy if carbon dioxide is present.
How can a limewater experiment show that expired air contains more carbon dioxide than inspired air?
Pass comparable amounts of inspired and expired air through limewater. The limewater turns cloudy faster with expired air.
What is breathing rate?
The number of breaths taken in a given time.
What is breathing depth?
The amount of air moved in each breath.
How does physical activity affect breathing rate and depth?
Both breathing rate and breathing depth increase.
Why does physical activity increase the need for faster, deeper breathing?
Working muscles respire more rapidly, requiring more oxygen and producing more carbon dioxide.
How does faster, deeper breathing affect air movement through the lungs?
It moves more air into and out of the lungs.
What comparison can be used to investigate the effect of physical activity on breathing?
Compare breathing rate and depth at rest with those after physical activity.
What should be kept consistent when measuring breathing at rest and after physical activity?
The way breathing rate and depth are observed or measured.
How are the external and internal intercostal muscles positioned relative to each other?
Both lie between the ribs. The external intercostals are nearer the outside of the chest wall; the internal intercostals lie beneath them.
What do the external intercostal muscles do during inhalation?
They contract, moving the ribs upwards and outwards.
What happens to the diaphragm during inhalation?
It contracts and flattens.
How do thoracic volume and pressure change during inhalation, and what happens to airflow?
Thoracic volume increases, pressure falls, and air enters the lungs.
What happens to the diaphragm during exhalation?
It relaxes and becomes more dome-shaped.
How do the ribs move during exhalation, and what can cause this movement during active exhalation?
They move downwards and inwards. During active exhalation, contraction of the internal intercostal muscles can pull them in this direction.
How do thoracic volume and pressure change during exhalation, and what happens to airflow?
Thoracic volume decreases, pressure rises, and air leaves the lungs.
What is the role of cartilage in the trachea during ventilation?
It supports the trachea and prevents it from collapsing, keeping the airway open.
Why does carbon dioxide concentration in the blood increase during physical activity?
Working muscles produce more carbon dioxide through respiration.
How does the brain respond when it detects increased carbon dioxide in the blood?
It causes breathing to become faster and deeper.
How does faster, deeper breathing increase carbon dioxide removal from the blood?
It moves more air into and out of the lungs, increasing carbon dioxide removal.
What do goblet cells in the airways produce?
Mucus.
What does mucus trap in the airways?
Inhaled particles and pathogens.
How do ciliated cells move trapped material away from the lungs?
Their hair-like cilia beat, moving mucus and trapped material towards the throat.
What is the protective effect of mucus production and ciliary movement working together?
They help prevent particles and pathogens from reaching the gas exchange surfaces.