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C3.2.1—Pathogens cause infectious diseases

Pathogens cause infectious diseases explains how a specific barrier, pathogen interaction, immune mechanism or treatment response contributes to protection against infectious disease.

Syllabus
First assessment 2025
Objective
C3.2.1
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2017
Most common paperPaper3
Typical marks2–3

Common command terms

  • Describe
  • Distinguish
  • Outline
  • Define
  • State
  • Explain

Scoring notes

Common mistake
Naming symptoms without linking them to the causative pathogen or transmission route.

Recent exam appearances

May 2017Paper3 ["HL"] · TZ220[ 3 ]C3.2.1—Pathogens cause infectious diseases
May 2014Paper3 ["HL"] · TZ18(b)[ 2 ]C3.2.1—Pathogens cause infectious diseases
May 2014Paper3 ["HL"] · TZ18(a)(i)[ 3 ]C3.2.1—Pathogens cause infectious diseases
November 2012Paper3 ["HL"] · TZ0F2(c)[ 2 ]C3.2.1—Pathogens cause infectious diseases
May 2012Paper3 ["HL"] · TZ1F3[ 6 ]C3.2.1—Pathogens cause infectious diseases
Practice this objective

Coverage 2012–2017 · Updated 16 Jul 2026

Concept essentials

  • Pathogens cause infectious diseases has to be linked to the exact pathogen, cell, molecule or population process involved.
  • The biological effect of pathogens cause infectious diseases depends on the sequence from trigger to protective outcome.
  • Clear distinctions within pathogens cause infectious diseases prevent confusion with neighbouring immune responses.
  • Evidence for pathogens cause infectious diseases is strongest when mechanism and consequence are explained together.
ConceptIB Biology HL