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C4.1.18—Allelopathy and antibiotics

Allelopathy and antibiotics explains how ecological evidence links organisms, resources and interactions to population size, distribution or community structure in a habitat.

Syllabus
First assessment 2025
Objective
C4.1.18
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks3

Common command terms

  • Explain
  • Identify

Scoring notes

Common mistake
Including abiotic factors in the definition of community instead of reserving them for ecosystem.

Recent exam appearances

May 2025Paper2 ["HL"] · TZ13(b)[ 3 ]C4.1.18—Allelopathy and antibiotics
Practice this objective

Coverage 2025–2025 · Updated 16 Jul 2026

Concept essentials

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