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.

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 appearing16%of analysed past papers

Latest appearanceNovember 2025

Most common paperPaper3

Most tested objectives

C2.1.6 (HL)—Transmembrane vs. intracellular receptors14 questions
C2.1.2 (HL)—Quorum sensing in bacteria13 questions
C2.1.3 (HL)—Functional categories in animals10 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