IB Biology HL B4.2.2 Oxygen Tolerance Questions

Explore how oxygen availability separates obligate aerobes, oxygen-sensitive obligate anaerobes and facultative anaerobes that switch pathways across environmental gradients in IB Biology HL B4.2.2.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Explain how oxygen availability selects microbial niches by supporting obligate aerobes while poisoning obligate anaerobes.
  • Interpret environmental or depth-gradient evidence to distinguish facultative anaerobes that switch between aerobic and anaerobic respiration when oxygen changes.

IB Biology HL B4.2.2 Oxygen Tolerance Questions question 1

[Maximum number: 2]

Marine sediments form at the bottom of oceans. These sediments contain organic material from the surface waters. Scientists analysed samples drilled from the floor of the north Pacific Ocean, representing 86 million years of sedimentation. Graph A shows the data for oxygen concentrations in 28 metres of sediment and graph B shows the oxygen consumption per cell in 22 metres of sediment measured in femtomoles ( fmol=10−15 mol\mathrm{fmol}=10^{-15} \mathrm{~mol} ).

Figure for Question IB Biology HL B4.2.2 Oxygen Tolerance Questions question 1 — IB Biology HL

Suggest reasons for the differences in oxygen consumption between the cells at 2 metres and at 22 metres.

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