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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.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

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 energyC1.3.2—CO₂ → glucoseC1.3.3—Oxygen as by-productC1.3.4—Photosynthetic pigment separationC1.3.5—Absorption of specific wavelengthsC1.3.6—Absorption vs. action spectraC1.3.7—Limiting factors investigationC1.3.8—CO₂ enrichment experimentsC1.3.9 (HL)—PhotosystemsC1.3.10 (HL)—Advantages of pigment arraysC1.3.11 (HL)—Photolysis of waterC1.3.12 (HL)—ATP production in thylakoidsC1.3.13 (HL)—NADP reductionC1.3.14 (HL)—Thylakoids as light-dependent systemsC1.3.15 (HL)—Carbon fixation by RubiscoC1.3.16 (HL)—Triose phosphate synthesisC1.3.17 (HL)—RuBP regenerationC1.3.18 (HL)—Synthesis of other compoundsC1.3.19 (HL)—Interdependence of light and light-independent reactions

Question 1

[Maximum number: 8]

In ecosystems, energy is used to convert inorganic compounds into organic matter. Energy enters ecosystems through producers.

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

Question 2

[Maximum number: 9]

In water, shorter wavelengths of light such as blue and green penetrate deepest, and longer wavelengths of light penetrate less far. Red light does not reach depths of more than 50 m . Marine algae live at various water depths. Certain species of algae contain the pigments that enable them to adapt to life at different depths.

The graphs show the absorption and action spectra for two species of algae: Ulva taeniata, which is green, and Porphyra nereocystis, which is red.

Figure for Question 2 — IB Biology HL

Absorption / %

Figure for Question 2 — IB Biology HL
Figure for Question 2 — IB Biology HL

Question (a)

(a)

In each species, identify the colour of light that is used mainly for photosynthesis.

Ulva taeniata:

Porphyra nereocystis:

[ 2 ]

Question (b)

(b)

Deduce, with a reason, which algae lives at a greater depth.

[ 1 ]

Question (c)

(c)

Describe how the rate of photosynthesis could be measured in a marine alga, to produce an action spectrum.

[ 3 ]

Question (d)

(d)

Outline the structure and location of photosystems.

[ 2 ]

Question (e)

(e)

State the method used to separate photosynthetic pigments in a leaf extract.

[ 1 ]

Question 3

[Maximum number: 10]

Question (a)

(a)

Distinguish between the absorption of red light, blue light and green light by plants.

[ 4 ]

Question (b)

(b)

Outline how light intensity and concentration of carbon dioxide affect photosynthesis.

[ 6 ]
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