B3.1.2—Properties of gas-exchange surfaces

Efficient gas-exchange surfaces combine large area, thin permeable walls, moisture and maintained gradients so gases diffuse rapidly between air and blood.

Exam analysis

Chance of appearing2%of analysed past papers

Latest appearanceMay 2024

Most common paperPaper2

Typical marks3–4

Common command terms

State
Describe
Explain

Scoring notes

Common mistake: Listing alveolar features without linking each feature to faster diffusion.

Recent exam appearances

May 2024Paper2 ["HL"] · TZ26(b)[ 3 ]B3.1.2—Properties of gas-exchange surfaces

November 2016Paper2 ["HL"] · TZ06(b)[ 4 ]B3.1.2—Properties of gas-exchange surfaces

Practice this objective

Coverage 2016–2024 · Updated 15 Jul 2026

Concept essentials

Large surface area increases the amount of gas that can diffuse at once.
Thin exchange walls reduce the distance oxygen and carbon dioxide must cross.
Moist surfaces allow respiratory gases to dissolve before diffusion.
Ventilation and blood flow maintain steep concentration gradients across alveoli.

ConceptIB Biology HL