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IB Biology HL D4.2 Stability and Change Questions

Practise IB Biology HL D4.2 by analysing ecosystem data, making resource-management decisions and predicting change during primary succession.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Evaluate mesocosm designs against field studies using controls, replication and environmental realism.
  • Explain how sunlight supplies energy and decomposers recycle nutrients in sustainable ecosystems.
  • Define keystone species and predict community changes after its removal, including trophic cascades.
  • Assess fish-stock management by comparing harvest with replacement and recruitment rates.
  • Evaluate agricultural trade-offs involving soil, phosphate, fertilizer runoff and straw energy.
  • Trace nutrient enrichment through algal growth, decomposition, rising BOD and hypoxia.
  • Interpret food-web data to trace pollutant bioaccumulation and biomagnification.
  • Evaluate DDT or mercury use by weighing disease or dietary benefits against ecological risks.
  • Explain marine plastic impacts through ingestion, entanglement, currents and toxin transfer.
  • Explain how rewilding restores trophic interactions, connectivity and biodiversity.
  • Trace primary succession from bare substrate through soil development to greater biomass and diversity.

Covered syllabus points

D4.2.1—Stability of natural ecosystemsD4.2.2—Requirements for stabilityD4.2.3—Amazon rainforest deforestationD4.2.4—Mesocosm modelD4.2.5—Keystone speciesD4.2.6—Sustainable resource harvestingD4.2.7—Agriculture sustainability factorsD4.2.8—EutrophicationD4.2.9—BiomagnificationD4.2.10—Plastic pollution of oceansD4.2.11—RewildingD4.2.12 (HL)—Ecological successionD4.2.13 (HL)—Changes during primary successionD4.2.14 (HL)—Cyclical successionD4.2.15 (HL)—Climax communities and arrested succession

Question 1

[Maximum number: 4]

Outline the features of ecosystems that make them sustainable.

Question 2

[Maximum number: 1]

Satellite imagery has been used for many years in the Amazon rainforest to monitor deforestation. Annual deforestation can be calculated using data from several satellites that have varying levels of accuracy. The graph shows the area of the Amazon rainforest that was deforested each year from 2001 to 2019, calculated using satellite images.

Figure for Question 2 — IB Biology HL

The Amazon rainforest currently releases very large amounts of water vapour into the atmosphere through transpiration. Suggest one consequence of this.

Question 3

[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 3 — IB Biology HL
Figure for Question 3 — IB Biology HL

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

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