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C2.1 Chemical signalling [HL only]

Chemical signalling coordinates cell responses through ligands, receptors and transduction pathways that convert external or internal signals into specific physiological effects.

Syllabus
First assessment 2025
Topic
C2.1
Level
HL

What you’ll learn

14 learning objectives

Choose one objective for a focused lesson, or study the complete topic.

Exam analysis

An aggregate view of how the complete C2.1 Chemical signalling [HL only] appears across past papers.

Chance of appearing28%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3

Most tested objectives

  1. C2.1.6 (HL)—Transmembrane vs. intracellular receptors14 questions
  2. C2.1.3 (HL)—Functional categories in animals6 questions
  3. C2.1.1 (HL)—Receptors as proteins4 questions

Common question formats

  • Calculation
  • Comparison
  • Data analysis
  • Diagram interpretation
  • Process explanation
  • Structured response
  • Definition or recall

Exam question appearances

November 2025Paper2 ["HL"] · TZ39(a)[ 4 ]C2.1.1 (HL)—Receptors as proteins
November 2025Paper1A ["HL"] · TZ117[ 1 ]C2.1.2 (HL)—Quorum sensing in bacteria
May 2025Paper2 ["HL"] · TZ15(b)[ 3 ]C2.1.10 (HL)—Epinephrine (adrenaline) mechanism
May 2025Paper1A ["HL"] · TZ218[ 1 ]C2.1.10 (HL)—Epinephrine (adrenaline) mechanism
November 2024Paper2 ["HL"] · TZ02(e)[ 1 ]C2.1.3 (HL)—Functional categories in animals
Practice this topic

4 original exam-style questions based on the patterns above.

Coverage 2012–2025 · Updated 15 Jul 2026

Study checklistC2.1 Chemical signalling [HL only]