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B3.1.1—Gas exchange as vital function

Gas exchange supports aerobic respiration by supplying oxygen to cells and removing carbon dioxide from organisms through diffusion across suitable exchange surfaces.

Syllabus
First assessment 2025
Objective
B3.1.1
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2015
Most common paperPaper3
Typical marks2

Common command terms

  • Describe
  • Distinguish
  • Explain
  • Outline

Scoring notes

Common mistake
Confusing ventilation with gas exchange or with cell respiration rather than separating air movement, diffusion and energy release.

Recent exam appearances

May 2015Paper3 ["HL"] · TZ213(a)(ii)[ 2 ]B3.1.1—Gas exchange as vital function
Practice this objective

Coverage 2015–2015 · Updated 15 Jul 2026

Concept essentials

  • Aerobic cell respiration requires oxygen and produces carbon dioxide that must be removed.
  • Ventilation moves the external medium, while gas exchange is diffusion of gases across a surface.
  • Unicellular organisms can exchange gases by simple diffusion across the cell membrane.
  • Large or active organisms require specialised surfaces because diffusion distance and demand increase.
ConceptIB Biology HL