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IB ESS SL 4.4.6 Eutrophication Sequence Questions

Trace nutrient enrichment, algal growth, oxygen depletion and ecosystem change.

Syllabus
First assessment 2026
Course
ESS SL
Level
SL

Exam points

  • outline the eutrophication sequence and distinguish nutrient inputs from natural cycles, agricultural fertilizer runoff and domestic wastewater
  • explain how excess nutrients cause algal growth, reduced light and photosynthesis, oxygen depletion through decomposition, hypoxia, organism death and possible positive feedback
  • apply and evaluate the sequence using map, lake or coastal evidence, considering long-term effects on tolerance, reproduction, food webs, ecosystem services and human activities

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Study 4.4.6—Eutrophication sequence conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB ESS SL 4.4.6 Eutrophication Sequence Questions question 1

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pH-tolerance ranges of freshwater organisms

Figure:pH-tolerance ranges of freshwater organisms

the pH-tolerance ranges of freshwater organisms below shows the ranges of pH over which different types of aquatic organisms in a small lake can survive.

Use the pH-tolerance ranges of freshwater organisms: the pH tolerance ranges of trout, bass, perch, frogs, salamanders, clams, crayfish, snails and mayfly in the small lake.

Explain why the populations of remaining organisms in the lake may decline in the long term.

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