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C1.3.1—Light energy → chemical energy

Photosynthesis captures light with pigments and converts it into chemical energy stored temporarily in ATP and ultimately in organic molecules.

Syllabus
First assessment 2025
Objective
C1.3.1
Level
SL

Exam analysis

Chance of appearing7%of analysed past papers
Latest appearanceMay 2022
Most common paperPaper2
Typical marks1–6

Common command terms

  • Identify
  • State
  • Outline
  • Describe
  • Explain
  • Distinguish

Recent exam appearances

May 2022Paper2 ["SL"] · TZ16(b)[ 5 ]C1.3.1—Light energy → chemical energy
May 2021Paper2 ["SL"] · TZ12(a)(i)[ 1 ]C1.3.1—Light energy → chemical energy
November 2020Paper2 ["SL"] · TZ05(b)[ 5 ]C1.3.1—Light energy → chemical energy
May 2019Paper2 ["SL"] · TZ18(c)[ 7 ]C1.3.1—Light energy → chemical energy
November 2018Paper3 ["SL"] · TZ01(b)(ii)[ 1 ]C1.3.1—Light energy → chemical energy

Coverage 2010–2022 · Updated 15 Jul 2026

Photosynthesis Stores Light Energy in Carbon Compounds

Photosynthesis converts light energy into chemical energy stored in organic carbon compounds. It supplies the carbon compounds and most of the chemical energy that enter ecosystems.

Photoautotroph Where chlorophyll captures light
plant or alga thylakoid membranes inside chloroplasts
cyanobacterium internal photosynthetic membranes; no chloroplast
Chlorophyll-containing thylakoids in a plant chloroplast and photosynthetic membranes in a cyanobacterium absorb light.

light absorbed by pigments → excited electrons → ATP and reduced NADP → CO₂ reduced into carbon compounds

SL Checkpoint: Read Photosynthesis as Matter, Energy and Evidence

light energy → excited pigment electrons → ATP and reduced NADP → CO₂ reduced using hydrogen from water → organic carbon compounds; photolysis of water releases O₂

  • A chromatogram separates pigments; Rf compares their movement under matched conditions.
  • An absorption spectrum measures captured wavelengths; an action spectrum measures whole-process rate.
  • A limiting-factor experiment changes one condition, controls the others and measures O₂ production or CO₂ uptake per unit time.

When a rate curve plateaus, identify which factor was relieved and which may now be limiting. When evaluating CO₂ enrichment, separate strong control from ecological realism and do not extrapolate beyond the tested conditions.

Light energy → chemical energy

[ 8 ]

Explain the processes by which light energy is converted into chemical energy.

Concept essentials

  • Chlorophyll and other pigments absorb light energy inside chloroplasts.
  • Light energy is converted into chemical energy during photosynthesis.
  • ATP and reducing power connect light capture to carbon compound formation.
  • Photosynthesis produces organic molecules that store usable chemical energy.