IGCSE Biology glossary
Diaphragm
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Definition
A sheet of muscle beneath the lungs that plays a key role in ventilation. During inhalation, the diaphragm contracts and flattens, increasing the volume of the thorax and decreasing pressure so air is drawn into the lungs. During exhalation it relaxes and domes upwards.
What to include in an exam answer
The diaphragm CONTRACTS and FLATTENS during inhalation (not 'moves down'). It RELAXES and DOMES UP during exhalation. Using the precise terms earns marks.
Example in context
Describe the role of the diaphragm during inhalation (2 marks): The diaphragm contracts and flattens, increasing the volume of the thoracic cavity. This decreases the air pressure inside the lungs, causing air to flow in.
Related syllabus topic
Gas exchange in humans