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C1.3 Photosynthesis

Photosynthesis converts light energy into chemical energy by using pigments, thylakoid reactions and Calvin-cycle carbon fixation to build organic compounds from carbon dioxide.

Syllabus
First assessment 2025
Topic
C1.3
Level
SL

Exam analysis

Chance of appearing51%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–2

Most tested objectives

Common question formats

  • Calculation
  • Comparison
  • Data analysis
  • Diagram interpretation
  • Experimental design
  • Graph interpretation
  • Process explanation
  • Structured response
  • Definition or recall

Recent exam appearances

November 2025Paper1A ["SL"] · TZ15[ 1 ]C1.3.7—Limiting factors investigation
November 2025Paper1A ["SL"] · TZ35[ 1 ]C1.3.7—Limiting factors investigation
May 2025Paper1A ["SL"] · TZ25[ 1 ]C1.3.2—CO₂ → glucose
May 2025Paper1A ["SL"] · TZ14[ 1 ]C1.3.7—Limiting factors investigation
November 2024Paper1 ["SL"] · TZ18[ 1 ]C1.3.3—Oxygen as by-product
Practice this topic

Coverage 2010–2025 · Updated 15 Jul 2026

Objective notes

8 learning objectives
C1.3.1Light energy → chemical energy

• Photosynthesis converts light energy into chemical energy in carbon compounds

• Photoautotrophs use chlorophyll in chloroplasts or cyanobacterial membranes

C1.3.2CO₂ → glucose

• Carbon dioxide is reduced to carbohydrate using hydrogen from water

• Glucose represents the main stored product, though many compounds are synthesized

C1.3.3Oxygen as by-product

• Oxygen is released from photolysis of water, not directly from CO₂

• Oxygenic photosynthesis occurs in plants, algae, and cyanobacteria

C1.3.4Photosynthetic pigment separation

• Paper chromatography separates chlorophylls and accessory pigments

• Rf values compare pigment movement relative to solvent front

C1.3.5Absorption of specific wavelengths

• Chlorophyll and accessory pigments absorb specific wavelengths

• Absorbed light excites electrons for light-dependent reactions

C1.3.6Absorption vs. action spectra

• Absorption spectra show wavelengths absorbed by pigments

• Action spectra show wavelengths most effective for photosynthesis rate

C1.3.7Limiting factors investigation

• Light intensity, CO₂ concentration, and temperature can limit photosynthesis

• Investigations change one variable and estimate rate from O₂ production or CO₂ uptake

C1.3.8CO₂ enrichment experiments

• CO₂ enrichment tests whether increased CO₂ raises photosynthesis or growth

• Greenhouse and FACE experiments compare realistic crop and ecosystem responses

ConceptIB Biology SL