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IB Biology HL D4.2 Ecosystem Stability and Change Question Bank

Practise IB Biology HL D4.2 with ecosystem data questions on stability, succession, biomagnification, pollution, keystone species and sustainable resource use.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • analyse stability requirements in mesocosms using nutrient cycles, energy flow and abiotic conditions
  • explain eutrophication, biomagnification and plastics through trophic transfer and ecosystem effects
  • evaluate succession, keystone species and resource harvesting using population or diversity data

D4.2 Stability and change question 1

[Maximum number: 4]

Outline the features of ecosystems that make them sustainable.

D4.2 Stability and change question 2

[Maximum number: 2]

An investigation into food web interactions was conducted in mesocosms in the Mediterranean Sea, off the coast of France. The effects of the addition of soil and fish on bacterial populations were tested.

Figure for Question D4.2 Stability and change question 2 — IB Biology HL
Figure for Question D4.2 Stability and change question 2 — IB Biology HL

Suggest advantages of undertaking this experiment in the sea rather than in the laboratory.

D4.2 Stability and change question 3

[Maximum number: 2]

The gut of a healthy human contains more than 1000 species of bacteria. Some of these species are shown in the cladogram.

Figure for Question D4.2 Stability and change question 3 — IB Biology HL

Scientists have found that B. fragilis and B. stercosis are keystone species in the human gut ecosystem.

Define keystone species.

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