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C4.1.17—Top-down vs. bottom-up control

Top-down versus bottom-up control explains how ecological evidence links organisms, resources and interactions to population size, distribution or community structure in a habitat.

Syllabus
First assessment 2025
Objective
C4.1.17
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–3

Common command terms

  • Explain
  • Describe
  • Identify
  • Outline

Scoring notes

Common mistake
Confusing a population with a community or with all organisms in an ecosystem.

Recent exam appearances

November 2025Paper1A ["HL"] · TZ336[ 1 ]C4.1.17—Top-down vs. bottom-up control
November 2018Paper3 ["HL"] · TZ014(c)[ 2 ]C4.1.17—Top-down vs. bottom-up control
November 2018Paper3 ["HL"] · TZ014(b)[ 1 ]C4.1.17—Top-down vs. bottom-up control
May 2018Paper3 ["HL"] · TZ215(c)[ 3 ]C4.1.17—Top-down vs. bottom-up control
May 2018Paper3 ["HL"] · TZ215(b)[ 2 ]C4.1.17—Top-down vs. bottom-up control
Practice this objective

Coverage 2016–2025 · Updated 16 Jul 2026

Concept essentials

  • Top-down versus bottom-up control must be linked to the correct ecological unit, method or species interaction.
  • The evidence for top-down versus bottom-up control depends on measurable abundance, distribution, survival or resource patterns.
  • Top-down versus bottom-up control is clearest when cause, ecological process and population outcome are kept distinct.
  • Field or graph evidence for top-down versus bottom-up control needs biological interpretation, not values alone.
ConceptIB Biology HL