C2.1.1 (HL)—Receptors as proteins
Receptors are proteins with complementary binding sites that allow only target cells carrying the matching receptor to respond to chemical signals.
- Syllabus
- First assessment 2025
- Objective
- C2.1.1
- Level
- HL
Exam analysis
Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–4
Common command terms
- Describe
- Explain
Recent exam appearances
November 2025Paper2 ["HL"] · TZ39(a)[ 4 ]C2.1.1 (HL)—Receptors as proteins
November 2023Paper3 ["HL"] · TZ223(b)[ 3 ]C2.1.1 (HL)—Receptors as proteins
November 2023Paper3 ["HL"] · TZ123(b)[ 3 ]C2.1.1 (HL)—Receptors as proteins
May 2022Paper1 ["HL"] · TZ125[ 1 ]C2.1.1 (HL)—Receptors as proteins
Practice this objective
Coverage 2022–2025 · Updated 15 Jul 2026
Concept essentials
- Receptors are proteins with specific ligand-binding sites.
- Only cells with the matching receptor respond to a signalling chemical.
- Peptide hormones usually bind to receptors in the plasma membrane.
- Ligand-receptor binding can initiate intracellular signal transduction.