IGCSE Biology glossary
Bronchiole
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Definition
A small airway that branches from the bronchi inside the lungs. Bronchioles have smooth muscle in their walls but no cartilage, allowing them to constrict or dilate to control airflow. They end in clusters of alveoli.
What to include in an exam answer
Bronchioles have smooth muscle but no cartilage (unlike the trachea and bronchi). Contraction of smooth muscle narrows the bronchioles, as occurs in asthma.
Example in context
Explain why a person with asthma has difficulty breathing (2 marks): The smooth muscle in the bronchiole walls contracts, narrowing the airways. This restricts airflow to and from the alveoli, making it harder to breathe.
Related syllabus topic
Gas exchange in humans