B4.2.2—Oxygen tolerance
Oxygen tolerance shapes microbial niches because some organisms require oxygen, some are poisoned by it and others can switch pathways.
- Syllabus
- First assessment 2025
- Objective
- B4.2.2
- Level
- SL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1
Recent exam appearances
May 2025Paper1B ["SL"] · TZ22(c)[ 1 ]B4.2.2—Oxygen tolerance
November 2020Paper1 ["SL"] · TZ018[ 1 ]B4.2.2—Oxygen tolerance
Practice this objective
Coverage 2020–2025 · Updated 15 Jul 2026
Concept essentials
- Obligate aerobes require oxygen for survival.
- Obligate anaerobes live where oxygen is absent.
- Facultative anaerobes can switch between aerobic and anaerobic metabolism.
- Methane production is favoured in anaerobic environments.