IB Biology HL C1.3 Photosynthesis Questions

Practise IB Biology HL C1.3 by linking pigments and limiting factors to photosystems, photophosphorylation and carbon fixation evidence.

136 questions in this syllabus scope, with question parts counted together.

Exam analysis

HL · 2010–2025

Papers with this topic60 / 117in the analysed sample

Latest appearanceNovember 2025

Tagged question parts90

Paper types5

Most tested objectives

C1.3.15 (HL)—Carbon fixation by Rubisco13 papers
C1.3.7—Limiting factors investigation11 papers
C1.3.12 (HL)—ATP production in thylakoids8 papers
C1.3.6—Absorption vs. action spectra7 papers
C1.3.11 (HL)—Photolysis of water6 papers

Common question formats

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

Recent exam appearances

November 2025Paper 1B HL · TZ3Q3(a), 3(b), 3(c), 3(d), 3(e)[ 9 ]

November 2025Paper 1A HL · TZ3Q7[ 1 ]

May 2025Paper 2 HL · TZ3Q10(b)[ 7 ]

117 papers analysed · Tagging incomplete

Exam points

Explain how Photosystem II photolyses water to replace electrons and release oxygen and hydrogen ions; identify oxygen as a product of oxygenic photosynthesis.
Separate photosynthetic pigments by chromatography and describe the procedure or calculate and interpret Rf values to identify pigments.
Compare absorption and action spectra, interpret wavelength evidence and relate peaks to photosynthetic rate.
Interpret limiting-factor curves and evaluate controlled photosynthesis experiments, including temperature, CO₂ enrichment and FACE evidence.
Identify photosystems and pigment arrays in thylakoid membranes, then trace light-excited electron movement from Photosystem II to Photosystem I.
Explain electron transfer, proton pumping and proton flow through ATP synthase as chemiosmosis and photophosphorylation.
Explain how Photosystem I reduces NADP and how light-dependent ATP and reduced NADP support the Calvin cycle.
Trace Calvin-cycle carbon from Rubisco fixation of CO₂ to RuBP into glycerate 3-phosphate, then its ATP- and reduced-NADP-dependent reduction to triose phosphate.
Explain RuBP regeneration and use Calvin-cycle stoichiometry to relate triose phosphate, glucose formation and the regenerated acceptor.

Covered syllabus points

C1.3.1—Light energy → chemical energy C1.3.2—CO₂ → glucose C1.3.3—Oxygen as by-product C1.3.4—Photosynthetic pigment separation C1.3.5—Absorption of specific wavelengths C1.3.6—Absorption vs. action spectra C1.3.7—Limiting factors investigation C1.3.8—CO₂ enrichment experiments C1.3.9 (HL)—Photosystems C1.3.10 (HL)—Advantages of pigment arrays C1.3.11 (HL)—Photolysis of water C1.3.12 (HL)—ATP production in thylakoids C1.3.13 (HL)—NADP reduction C1.3.14 (HL)—Thylakoids as light-dependent systems C1.3.15 (HL)—Carbon fixation by Rubisco C1.3.16 (HL)—Triose phosphate synthesis C1.3.17 (HL)—RuBP regeneration C1.3.18 (HL)—Synthesis of other compounds C1.3.19 (HL)—Interdependence of light and light-independent reactions

Exam points

Explain how chlorophyll absorbs light and photosynthesis converts its energy into chemical energy in carbon compounds.
Identify chloroplasts or cyanobacterial membranes as sites where photoautotrophs use chlorophyll for photosynthesis.

[Maximum number: 1]

A broad bean is the seed of a species, Vicia faba, in the Fabaceae, a family of flowering plants. This family contains many species that are used as sources of food.

Once the germinated bean grows above the ground, state the process used by the bean in the production of starch.

Exam points

Explain that light-driven photolysis of water releases oxygen during photosynthesis; the oxygen does not come directly from carbon dioxide.
Identify plants, algae and cyanobacteria as organisms that carry out oxygenic photosynthesis.

Exam points

Explain how pigment solubility or affinity for the mobile and stationary phases separates photosynthetic pigments into distinct bands.
Calculate or interpret Rf as pigment distance divided by solvent-front distance, then compare values or colours with standards to identify pigments.
Describe the extraction and chromatographic procedure, including a suitable solvent, baseline spotting and development of separated bands.

[Maximum number: 1]

The diagram shows a chromatogram of the pigments in a leaf. Substance Z is known to have an $R_{f}$ of 0.5.

Solvent front

Sample applied

What are pigments X and Y ?

Chlorophyll a

Phaeophytin

Chlorophyll a

Carotene

Chlorophyll b

Carotene

Chlorophyll b

Chlorophyll a

Exam points

Compare chlorophyll and accessory-pigment absorption across red, blue and green wavelengths, including which light is reflected.
Interpret absorption-spectrum evidence to explain how absorbed wavelengths excite photosynthetic pigments and support photosynthesis.

[Maximum number: 3]

Describe how autotrophs absorb light energy.

Exam points

Compare absorption spectra with action spectra to explain how pigment wavelength absorption relates to photosynthetic rate.
Construct or interpret action-spectrum graphs, including wavelength peaks, troughs and differences among photosynthetic organisms.

[Maximum number: 1]

Which graph represents the action spectrum for a green plant receiving only blue light?

Exam points

Interpret photosynthesis data or curves to identify whether light intensity, carbon dioxide concentration or temperature is limiting the rate.
Describe controlled investigations that vary one factor and estimate photosynthesis rate from oxygen production or carbon dioxide uptake.
Explain how temperature changes photosynthesis rate, using enzyme activity evidence where relevant.

[Maximum number: 1]

The graph shows how the rate of photosynthesis of a green plant varies with $\mathrm{CO}_{2}$ concentration at two different light intensities. The temperature is kept constant at $20^{\circ} \mathrm{C}$ .

What is the limiting factor at X ?

Chlorophyll

Light intensity

Temperature

$\mathrm{CO}_{2}$ concentration

Exam points

Recognise that free-air CO₂ enrichment (FACE) experiments can provide data that better represent future photosynthesis rates.

[Maximum number: 1]

What is an advantage of free-air carbon dioxide enrichment experiments (FACE)?

The carbon dioxide uptake by plants is controlled.

Temperature can be controlled.

Water can be controlled.

Data can more accurately represent future rates of photosynthesis.

Exam points

Describe photosystems as pigment arrays embedded in thylakoid membranes, with antenna pigments and reaction-centre chlorophyll.
Explain how antenna pigments absorb a wider range of wavelengths and pass captured energy to reaction-centre chlorophyll.
Outline the relationship between Photosystem II and Photosystem I, including their order and link through electron carriers.

[Maximum number: 3]

There is a relationship between form and function in the diversity of molecules and of systems.

Outline the relationship between structure and function in photosystems.

No public sample questions are available for this syllabus point yet.

Exam points

Describe photolysis as the light-driven splitting of water at Photosystem II to produce electrons, protons and oxygen.
Explain how photolysis products contribute to the light-dependent reactions: electrons replace those lost from Photosystem II, protons contribute to the thylakoid gradient, and oxygen is released.

[Maximum number: 1]

The Hill reaction occurs when isolated chloroplasts are exposed to sunlight in the presence of DCPIP. DCPIP replaces NADP as the final electron acceptor for the light-dependent reactions of photosynthesis. What are products of the Hill reaction?

$\mathrm{H}_{2} \mathrm{O}$ and ATP

ATP and $\mathrm{CO}_{2}$

$\mathrm{O}_{2}$ and ATP

$\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$ and $\mathrm{O}_{2}$

Exam points

Explain how electron transport in the thylakoid membrane pumps protons into the thylakoid space, creating a proton gradient.
Describe how protons flow through ATP synthase to drive ADP phosphorylation and ATP production by chemiosmosis.

[Maximum number: 1]

Which structure in the chloroplast diagram is adapted to carry out chemiosmosis?

Exam points

Identify Photosystem I as the source of high-energy electrons used to reduce NADP in the light-dependent reactions.
Explain how NADP accepts electrons and H⁺ to form reduced NADP/NADPH.

[Maximum number: 1]

Which process does not take place in the stroma of chloroplasts?

Synthesis of carbohydrates

Fixation of carbon

Reduction of NADP

Synthesis of ribulose bisphosphate

Exam points

Identify Photosystem II, Photosystem I and the thylakoid space in a labelled thylakoid diagram, using electron-flow direction to distinguish the photosystems.

[Maximum number: 1]

The diagram shows a section through a thylakoid. Electrons move from X to Y .

What do the letters X, Y and Z represent?

photosystem I

photosystem II

thylakoid space

photosystem II

photosystem I

thylakoid space

ATP synthase

photosystem II

stroma

photosystem II

ATP synthase

stroma

Exam points

Explain how Rubisco catalyses CO₂ fixation to RuBP, forming glycerate 3-phosphate in the Calvin cycle.
Interpret radioactive-carbon evidence from Calvin's experiments to identify glycerate 3-phosphate as the first stable product of carbon fixation.

[Maximum number: 1]

The cycle shows part of the light-independent reactions in photosynthesis.

What occurs in Step 1?

ATP is formed for Step 2.

Rubisco catalyses the hydrolysis of ribulose bisphosphate.

A carboxylase catalyses the carboxylation of ribulose bisphosphate.

NADP is converted to reduced NADP.

Exam points

Explain how glycerate 3-phosphate is reduced to triose phosphate using ATP and hydrogen from reduced NADP.
Interpret GP, TP and RuBP data in darkness to explain how reduced availability of ATP and reduced NADP limits GP-to-TP conversion.

[Maximum number: 1]

A photosynthesis experiment was set up in both light and dark conditions to determine the variations in relative concentrations of glycerate-3-phosphate (GP), triose phosphate (TP) and ribulose bisphosphate (RuBP).

What explains the results obtained in the dark conditions?

TP and RuBP from the light-dependent reaction are used to synthesize GP.

Less ATP and reduced NADP (NADPH) are available to convert GP to TP.

There is a low carbon dioxide supply for carbon fixation.

The enzyme Rubisco is only active in the presence of light.

Exam points

Calculate the number of RuBP molecules regenerated when one glucose molecule is formed in the Calvin cycle (six RuBP molecules).

[Maximum number: 1]

The Calvin cycle continues throughout the life of a plant. In this cycle, triose phosphate is produced, which is used to form glucose.

In total, how many RuBP molecules are regenerated in the process of creating one glucose molecule?

Exam points

Explain how starch accumulates when plants photosynthesise for longer periods, using evidence from end-of-day starch concentrations.
Explain how sucrose produced in leaves moves to sink tissues and is converted into starch for storage.

[Maximum number: 3]

The diagram shows the development of potato plants (Solanum tuberosum) over 14 weeks. New tubers start growing from week 9. These are modified underground stems serving as a starch reserve and bearing buds from which new plants arise.

Scientists planted several potato plants in a greenhouse. The sucrose and amino acids in potato plant phloem exudates were measured during several weeks.

Suggest reasons for different amounts of sucrose in the leaf phloem sap of the potato plants.

Exam points

Identify ATP and reduced NADP/NADPH as light-dependent products used in the Calvin cycle.
Explain how ATP supplies energy and reduced NADP supplies reducing power for glycerate 3-phosphate reduction and RuBP regeneration.

[Maximum number: 1]

Which products of the light-dependent reactions are used in the Calvin cycle?

$\mathrm{O}_{2}$ and hydrogen ions

ATP and $\mathrm{CO}_{2}$

Electrons and reduced NADP

ATP and reduced NADP

Exam analysis

Most tested objectives

Common question formats

Recent exam appearances

Covered syllabus points

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