Q BankQuestion BankDocsDocuments

C2.1.2 (HL)—Quorum sensing in bacteria

Quorum sensing lets bacteria coordinate gene expression when secreted signalling molecules indicate that population density has reached a threshold, linking signal detection to a specific target-cell response.

Syllabus
First assessment 2025
Objective
C2.1.2
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–4

Common command terms

  • State
  • Determine
  • Compare
  • Deduce
  • Explain
  • Define
  • Outline

Recent exam appearances

November 2025Paper1A ["HL"] · TZ117[ 1 ]C2.1.2 (HL)—Quorum sensing in bacteria
May 2024Paper3 ["HL"] · TZ22(b)[ 2 ]C2.1.2 (HL)—Quorum sensing in bacteria
May 2019Paper3 ["HL"] · TZ19(c)[ 4 ]C2.1.2 (HL)—Quorum sensing in bacteria
May 2019Paper3 ["HL"] · TZ210(a)(i)[ 2 ]C2.1.2 (HL)—Quorum sensing in bacteria
Practice this objective

Coverage 2019–2025 · Updated 15 Jul 2026

Concept essentials

  • Quorum sensing is triggered when bacterial signal concentration reflects sufficient population density.
  • Bacteria use quorum sensing to coordinate behaviours such as luminescence and biofilm formation.
  • Biofilms can increase survival under physical, chemical or nutritional stress.
  • Quorum-sensing data must be interpreted from density, luminescence or strain-comparison evidence.
ConceptIB Biology HL