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C1.3.6—Absorption vs. action spectra

Absorption spectra show pigment light absorption, while action spectra show how effectively each wavelength drives photosynthesis in living systems, connecting the mechanism to observable photosynthesis evidence.

Syllabus
First assessment 2025
Objective
C1.3.6
Level
HL

Exam analysis

Chance of appearing5%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–2

Common command terms

  • Sketch
  • Draw
  • Explain
  • Compare
  • Contrast
  • Predict
  • Deduce
  • Identify

Recent exam appearances

November 2025Paper1B ["HL"] · TZ33(b)[ 1 ]C1.3.6—Absorption vs. action spectra
November 2025Paper1B ["HL"] · TZ33(a)[ 2 ]C1.3.6—Absorption vs. action spectra
November 2022Paper1 ["HL"] · TZ08[ 1 ]C1.3.6—Absorption vs. action spectra
May 2022Paper1 ["HL"] · TZ27[ 1 ]C1.3.6—Absorption vs. action spectra
November 2021Paper1 ["HL"] · TZ08[ 1 ]C1.3.6—Absorption vs. action spectra
Practice this objective

Coverage 2013–2025 · Updated 15 Jul 2026

Concept essentials

  • Absorption spectra measure light absorbed by pigments at each wavelength.
  • Action spectra measure photosynthetic activity at each wavelength.
  • Action spectra usually reflect the combined absorption of several pigments.
  • Blue and red wavelengths often produce high photosynthetic activity in green plants.
ConceptIB Biology HL