Photosynthesis: A Level Biology questions with answers
Free Photosynthesis questions for A Level Biology (9700), part of Energy & control. Each question has the answer and the marking points an examiner would look for.
The Calvin cycle uses products of the light-dependent stage.
(a)
Describe the role of rubisco.
[2]
(b)
Explain why the concentration of RuBP increases when CO₂ concentration falls.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
fixes CO₂ with RuBP to form GP
rubisco catalyses the combination of CO₂ with RuBP B1 forming two molecules of GP B1
2
(b)
RuBP not used but still regenerated
less RuBP combines with CO₂ B1 but RuBP is still regenerated from TP B1
2
Question 2Structured · 11 marksA* challenge
(a)
Describe the light-independent stage of photosynthesis (the Calvin cycle).
[5]
(b)
Explain the effect of reducing light intensity on the concentrations of GP and RuBP.
[3]
(c)
Explain why C4 plants such as maize are more productive than C3 plants in hot climates.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
CO2 fixed by RuBP using rubisco forming two GP; GP reduced to TP using ATP and reduced NADP; some TP used to make glucose; most TP regenerates RuBP using ATP
RuBP + CO2 catalysed by rubisco B1 2 GP formed B1 GP reduced to TP using reduced NADP B1 ATP used B1 RuBP regenerated B1
5
(b)
less ATP and reduced NADP from light-dependent stage; GP not converted to TP so GP increases; RuBP not regenerated so RuBP decreases
less ATP/reduced NADP B1 GP accumulates B1 RuBP falls B1
3
(c)
CO2 fixed by PEP carboxylase in mesophyll; delivered to bundle sheath at high concentration; rubisco isolated from O2 so photorespiration minimised
PEP carboxylase fixes CO2B1 high CO2 in bundle sheath cells B1 less photorespiration B1
3
Question 3Structured · 13 marks
Pigments are extracted from a leaf and separated by thin-layer chromatography. The solvent moves 9.0 cm from the origin. Table 3.1 shows the Rf values of four photosynthetic pigments.
pigment
carotene
xanthophyll
chlorophyll a
chlorophyll b
Rf value
0.95
0.70
0.65
0.45
Table 3.1
(a)
One spot moves 5.9 cm from the origin. Calculate its Rf value and identify the pigment.
[2]
(b)
Explain why a plant has several different photosynthetic pigments.
[2]
(c)
Describe the role of chlorophyll a in the photosystems.
[2]
(d)
Distinguish between an absorption spectrum and an action spectrum.
[2]
(e)
Describe cyclic photophosphorylation.
[3]
(f)
Explain why the origin line is drawn in pencil and kept above the level of the solvent.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
0.66; chlorophyll a
Rf = 5.9 ÷ 9.0 = 0.66 B1 chlorophyll a (ft their Rf) B1
2
(b)
absorb different wavelengths; wider range of light used
each pigment absorbs light of different wavelengths B1 so a wider range of wavelengths can be used for photosynthesis B1
2
(c)
primary pigment in reaction centre; emits excited electrons
chlorophyll a is the primary pigment at the reaction centre B1 it absorbs light / receives energy from accessory pigments and emits excited electrons (photoactivation) B1
2
(d)
absorption: light absorbed by pigment at each wavelength; action: rate of photosynthesis at each wavelength
absorption spectrum shows how much light each pigment absorbs at each wavelength B1 action spectrum shows the rate of photosynthesis at each wavelength B1
2
(e)
PSI only; electron returns via ETC; ATP made, no reduced NADP
Any 3 of: involves photosystem I only; excited electron passes along electron carriers and returns to PSI; energy used to make ATP (by chemiosmosis); no reduced NADP or oxygen produced B3
3
(f)
ink would dissolve and run; pigments would dissolve into solvent
pencil (graphite) does not dissolve in the solvent, whereas ink would separate B1 if the spot were below the solvent, pigments would dissolve into the solvent instead of moving up B1
2
Question 4Structured · 11 marks
Fig. 4.1 shows the rate of photosynthesis of a plant at two concentrations of carbon dioxide, at 25 °C.
Fig. 4.1
(a)
Use Fig. 4.1 to state the factor limiting the rate of photosynthesis at a light intensity of 8 units. Explain your answer.
[2]
(b)
Explain the difference between the two curves at light intensities above 60 units.
[3]
(c)
Calculate the percentage increase in the maximum rate when the carbon dioxide concentration is raised.
[2]
(d)
Suggest why increasing the temperature from 25 °C to 30 °C may increase the maximum rate at 0.10% carbon dioxide.
[2]
(e)
Name the two products of the light-dependent reactions that are used in the Calvin cycle.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
light intensity
light intensity B1 the two curves are (almost) the same here and the rate rises as light intensity rises, so changing CO₂ concentration has (almost) no effect B1
2
(b)
CO₂ limiting at 0.04%; more CO₂ fixed by rubisco; more GP / TP made
at 0.04% carbon dioxide concentration is the limiting factor (allow: at 0.10% another factor, e.g. temperature, becomes limiting) B1 with more CO₂, rubisco fixes more CO₂ with RuBP B1 so more GP and triose phosphate are made per unit time B1
enzymes of Calvin cycle e.g. rubisco faster; more kinetic energy
the light-independent reactions are enzyme-controlled (rubisco) B1 more kinetic energy gives more enzyme–substrate collisions, until the optimum temperature B1
2
(e)
ATP; reduced NADP
ATP B1 reduced NADP B1
2
Question 5Structured · 11 marks
A student measures the rate of photosynthesis of a water plant at different temperatures, with light intensity and carbon dioxide concentration kept high.
temperature / °C
10
15
20
25
30
35
40
rate / arbitrary units
8
14
22
28
30
22
8
Table 5.1
(a)
Describe the effect of temperature on the rate of photosynthesis.
[3]
(b)
Explain the shape of the curve between 10 °C and 30 °C.
[2]
(c)
Suggest why the rate falls above 30 °C.
[2]
(d)
Calculate the percentage decrease in rate between 30 °C and 40 °C.
[2]
(e)
Explain why it is important to keep light intensity and CO₂ concentration high in this investigation.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
increases to 30 °C, optimum; decreases above; data quoted
rate increases from 10 °C to a maximum at 30 °C B1 decreases at higher temperatures B1 data quoted B1
3
(b)
enzymes (rubisco) in Calvin cycle; more kinetic energy, more enzyme–substrate complexes
Calvin cycle is controlled by enzymes such as rubisco B1 more kinetic energy gives more successful collisions / enzyme–substrate complexes B1
2
(c)
enzymes denature; stomata close / photorespiration increases
enzymes begin to denature B1 rubisco binds oxygen more (photorespiration increases) B1
2
(d)
73.3%
(30 − 8)/30 × 100 M1 73.3% A1
2
(e)
so temperature is the limiting factor
to ensure temperature is the only limiting factor B1 otherwise light or CO₂ could limit the rate B1
2
Question 6Structured · 13 marks
This question is about photosynthesis.
(a)
Describe the role of photosystems in cyclic and non-cyclic photophosphorylation.
[4]
(b)
Describe the Calvin cycle.
[4]
(c)
Photosynthetic pigments were separated by thin-layer chromatography. The solvent front moved 4.0 cm and one pigment moved 2.9 cm. Calculate its Rf value.
[2]
(d)
Explain why the rate of photosynthesis levels off as light intensity increases, and how a greenhouse grower could use limiting factors.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
light excites electrons in PSII and PSI; non-cyclic: photolysis, ATP and reduced NADP; cyclic: PSI only, ATP only
light energy is absorbed by chlorophyll in photosystems, exciting electrons B1 in non-cyclic photophosphorylation electrons pass from PSII via carriers to PSI then to NADP, producing ATP and reduced NADP B1 photolysis of water replaces electrons in PSII B1 in cyclic photophosphorylation electrons from PSI return to PSI, producing only ATP B1
4
(b)
CO₂ + RuBP by rubisco → 2 GP; GP reduced to TP using ATP and NADPH; some TP → glucose; RuBP regenerated using ATP
carbon dioxide combines with RuBP, catalysed by rubisco B1 forming two molecules of GP B1 GP is reduced to triose phosphate using ATP and reduced NADP B1 some TP used to regenerate RuBP (using ATP) and some to make glucose / other compounds B1
4
(c)
0.72
2.9/4.0 M1 0.72 A1
2
(d)
another factor limiting (CO₂ / temperature); increase CO₂ or temperature to raise rate
at high light intensity another factor (CO₂ concentration or temperature) limits the rate B1 growers increase CO₂ (paraffin burners) or temperature B1 only to the point where cost is justified by the increased yield B1
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Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in