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C1.3.9 (HL)—Photosystems

Photosystems are pigment-protein arrays in thylakoid membranes that capture light and pass excited electrons through linked reaction centres, connecting the mechanism to observable photosynthesis evidence.

Syllabus
First assessment 2025
Objective
C1.3.9
Level
HL

Exam analysis

Chance of appearing3%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–3

Common command terms

  • Outline

Recent exam appearances

November 2025Paper1B ["HL"] · TZ33(d)[ 2 ]C1.3.9 (HL)—Photosystems
May 2025Paper2 ["HL"] · TZ210(b)[ 3 ]C1.3.9 (HL)—Photosystems
November 2020Paper1 ["HL"] · TZ030[ 1 ]C1.3.9 (HL)—Photosystems
Practice this objective

Coverage 2020–2025 · Updated 15 Jul 2026

Concept essentials

  • Photosystems are located in thylakoid membranes.
  • Photosystem II passes electrons through carriers toward Photosystem I.
  • Reaction centres receive energy from surrounding pigment arrays.
  • Accessory pigments broaden the wavelengths captured by a photosystem.
ConceptIB Biology HL