A-Level Biology Topic 13: Photosynthesis MCQs – 30 Practice Questions with Answers (Cambridge 9700)

Free practice for Cambridge International AS and A Level Biology 9700 on photosynthesis, with every question followed by a short explanation to help you check your understanding.

Chloroplasts and Pigments

Q1. In a eukaryotic cell, in which organelle does photosynthesis take place?

  • (A) nucleus
  • (B) mitochondrion
  • (C) chloroplast
  • (D) vacuole
Show Answer

Answer: C – Photosynthesis in eukaryotes occurs within chloroplasts.

Q2. Within a chloroplast, stacks of thylakoids are known as what?

  • (A) grana
  • (B) cristae
  • (C) stroma lamellae
  • (D) thylakoid pores
Show Answer

Answer: A – Thylakoids occur in stacks called grana.

Q3. Which part of the chloroplast is the site of the light-independent stage of photosynthesis?

  • (A) thylakoid space
  • (B) grana
  • (C) outer membrane only
  • (D) stroma
Show Answer

Answer: D – The light-independent stage takes place in the stroma, while the light-dependent stage takes place in the thylakoids.

Q4. Which part of the chloroplast is the site of the light-dependent stage of photosynthesis?

  • (A) stroma
  • (B) thylakoid membranes
  • (C) ribosomes of the chloroplast
  • (D) chloroplast envelope only
Show Answer

Answer: B – The light-dependent stage occurs in the thylakoids, whereas the light-independent stage occurs in the stroma.

Q5. Which of these is a chloroplast pigment involved in light absorption in the thylakoids?

  • (A) chlorophyll b
  • (B) haemoglobin
  • (C) melanin
  • (D) carotene-free starch
Show Answer

Answer: A – Chlorophyll a, chlorophyll b, carotene and xanthophyll are the chloroplast pigments named in the syllabus.

Q6. An absorption spectrum for a pigment shows what?

  • (A) the rate of photosynthesis at each wavelength
  • (B) the colour of light reflected by a leaf at each wavelength
  • (C) the amount of carbon dioxide used at each wavelength
  • (D) how much light of each wavelength the pigment absorbs
Show Answer

Answer: D – An absorption spectrum plots absorption against wavelength for a pigment.

Q7. An action spectrum for photosynthesis shows what?

  • (A) the amount of pigment present at each wavelength
  • (B) the rate of photosynthesis at each wavelength of light
  • (C) the absorption of light by a single pigment in solution
  • (D) the temperature change at each wavelength
Show Answer

Answer: B – An action spectrum shows how the rate of photosynthesis varies with wavelength.

Q8. Chlorophyll absorbs light most strongly in which regions of the visible spectrum?

  • (A) the green and yellow regions only
  • (B) the infrared region only
  • (C) the blue and red regions
  • (D) all wavelengths equally
Show Answer

Answer: C – Chlorophyll absorbs mainly blue and red light and reflects much green light, which is why leaves look green.

Q9. In chromatography of leaf pigments, what does an Rf value help a student to do?

  • (A) measure the rate of photosynthesis directly in a whole leaf over a full day
  • (B) count the number of chloroplasts in a cell
  • (C) measure the concentration of carbon dioxide in air
  • (D) identify a pigment by comparing its movement with known values
Show Answer

Answer: D – Rf values are used in the identification of separated chloroplast pigments.

Q10. During chromatography, a pigment that travels furthest up the paper relative to the solvent front has what?

  • (A) the highest Rf value of the pigments separated
  • (B) the lowest Rf value of the pigments separated
  • (C) no Rf value
  • (D) the same Rf value as every other pigment
Show Answer

Answer: A – Rf is the distance moved by the pigment divided by the distance moved by the solvent front, so the furthest pigment has the highest Rf.

The Light-Dependent Stage

Q11. What is produced by photolysis of water in the light-dependent stage?

  • (A) carbon dioxide and glucose
  • (B) oxygen, protons and electrons
  • (C) reduced NADP only, with no other products
  • (D) ATP only, with no other products
Show Answer

Answer: B – Photolysis of water, catalysed by the oxygen-evolving complex, releases oxygen, protons and electrons.

Q12. Which photosystems are involved in non-cyclic photophosphorylation?

  • (A) photosystem I only
  • (B) photosystem II only
  • (C) photosystem I and photosystem II
  • (D) neither photosystem
Show Answer

Answer: C – Non-cyclic photophosphorylation involves both photosystem I and photosystem II.

Q13. Which photosystem is involved in cyclic photophosphorylation?

  • (A) photosystem I only
  • (B) photosystem II only
  • (C) photosystem I and photosystem II together
  • (D) no photosystem at all
Show Answer

Answer: A – In cyclic photophosphorylation only photosystem I is involved.

Q14. What is synthesised in cyclic photophosphorylation, but not reduced NADP?

  • (A) glucose
  • (B) triose phosphate
  • (C) glycerate 3-phosphate
  • (D) ATP
Show Answer

Answer: D – Cyclic photophosphorylation synthesises ATP, while reduced NADP is not produced because electrons return to photosystem I.

Q15. What is photoactivation of chlorophyll?

  • (A) chlorophyll breaking down in bright light
  • (B) chlorophyll moving from the stroma to the grana
  • (C) light energy raising electrons in chlorophyll to a higher energy level
  • (D) water splitting chlorophyll molecules apart
Show Answer

Answer: C – Photoactivation is the excitation of electrons in chlorophyll by absorbed light energy.


Q16. As energetic electrons pass through the electron transport chain, what happens to the energy they release?

  • (A) it is stored directly as glucose in the thylakoid space
  • (B) it is used to transfer protons across the thylakoid membrane
  • (C) it is used to fix carbon dioxide in the grana
  • (D) it is lost as light from the chloroplast
Show Answer

Answer: B – Released energy is used to pump protons across the thylakoid membrane into the thylakoid space.

Q17. How do protons return from the thylakoid space to the stroma?

  • (A) by active transport through the chloroplast envelope
  • (B) by simple diffusion through the grana stacks
  • (C) by osmosis through the stroma lamellae
  • (D) by facilitated diffusion through ATP synthase
Show Answer

Answer: D – Protons return by facilitated diffusion through ATP synthase, providing energy for ATP synthesis.

Q18. Which two products of the light-dependent stage are used in the light-independent stage?

  • (A) ATP and reduced NADP
  • (B) oxygen and water
  • (C) ATP and carbon dioxide
  • (D) reduced NADP and glucose
Show Answer

Answer: A – ATP and reduced NADP made in the light-dependent stage supply energy and reducing power for the Calvin cycle.

Q19. What is the role of the oxygen-evolving complex in non-cyclic photophosphorylation?

  • (A) it fixes carbon dioxide to RuBP
  • (B) it regenerates RuBP from triose phosphate
  • (C) it catalyses the photolysis of water
  • (D) it absorbs green light for photosynthesis
Show Answer

Answer: C – The oxygen-evolving complex catalyses photolysis of water, replacing electrons lost from photosystem II.

Q20. Why is non-cyclic photophosphorylation described as non-cyclic?

  • (A) electrons travel in a circle back to photosystem I
  • (B) electrons from water do not return to the photosystem they left
  • (C) ATP is made without any electron flow
  • (D) water is formed again at the end of the pathway
Show Answer

Answer: B – In the non-cyclic pathway, electrons pass from water through both photosystems to NADP and do not return to their starting point.

The Calvin Cycle and Limiting Factors

Q21. In the Calvin cycle, which enzyme catalyses carbon dioxide fixation?

  • (A) ATP synthase
  • (B) chlorophyllase
  • (C) glycerate kinase
  • (D) rubisco
Show Answer

Answer: D – Rubisco catalyses the fixation of carbon dioxide by combination with ribulose bisphosphate (RuBP).

Q22. When carbon dioxide combines with RuBP, a 5-carbon compound, what is formed?

  • (A) two molecules of glycerate 3-phosphate, a 3-carbon compound
  • (B) one molecule of glucose directly
  • (C) two molecules of triose phosphate directly
  • (D) one molecule of ribulose bisphosphate only
Show Answer

Answer: A – Fixation of one carbon dioxide to one RuBP yields two molecules of glycerate 3-phosphate (GP).

Q23. In the Calvin cycle, glycerate 3-phosphate (GP) is reduced to what?

  • (A) ribulose bisphosphate (RuBP) directly
  • (B) glucose directly, with no other steps
  • (C) triose phosphate (TP)
  • (D) carbon dioxide
Show Answer

Answer: C – GP is reduced to triose phosphate (TP) in reactions involving reduced NADP and ATP.

Q24. What is needed to reduce GP to TP in the Calvin cycle?

  • (A) oxygen and water only
  • (B) reduced NADP and ATP
  • (C) carbon dioxide and light directly
  • (D) ADP and NADP only
Show Answer

Answer: B – Reduction of GP to TP uses reduced NADP and ATP from the light-dependent stage.

Q25. How is RuBP regenerated in the Calvin cycle?

  • (A) from TP in reactions that use ATP
  • (B) from GP without any energy input
  • (C) by photolysis of water in the stroma
  • (D) by direct absorption of light in the stroma
Show Answer

Answer: A – RuBP is regenerated from TP in reactions that use ATP, so the cycle can continue.

Q26. Which molecules can be made from triose phosphate (TP) leaving the Calvin cycle?

  • (A) only starch, with no other products
  • (B) only oxygen and water
  • (C) only chlorophyll pigments
  • (D) carbohydrates, lipids and amino acids
Show Answer

Answer: D – Calvin cycle intermediates are used to make other molecules; TP can give rise to carbohydrates, lipids and amino acids.

Q27. Which of these is a limiting factor of photosynthesis named in the syllabus?

  • (A) soil nitrogen concentration alone
  • (B) carbon dioxide concentration
  • (C) wind speed alone
  • (D) leaf thickness alone
Show Answer

Answer: B – Light intensity, carbon dioxide concentration and temperature are named as examples of limiting factors.

Q28. At low light intensity, increasing light intensity usually does what to the rate of photosynthesis?

  • (A) decreases it, because enzymes denature
  • (B) has no effect at any light intensity
  • (C) increases it, because light is the factor limiting the rate
  • (D) stops it completely at once
Show Answer

Answer: C – When light is limiting, more light allows a faster light-dependent stage and so a faster overall rate.

Q29. Why does a very high temperature eventually reduce the rate of photosynthesis?

  • (A) enzymes involved, including those of the Calvin cycle, begin to denature
  • (B) chlorophyll is converted to starch
  • (C) stomata open wider and wider without limit
  • (D) carbon dioxide is used up by photolysis
Show Answer

Answer: A – Above the optimum, enzymes denature, so the rate falls even though the light-dependent stage may still run.

Q30. In an investigation with a suspension of chloroplasts, DCPIP is used for what purpose?

  • (A) as a stain to count chloroplasts under the microscope
  • (B) as a buffer to hold the pH exactly constant
  • (C) as a source of carbon dioxide for the suspension
  • (D) as a redox indicator whose colour change shows the rate of the light-dependent stage
Show Answer

Answer: D – DCPIP and methylene blue are redox indicators used with chloroplast suspensions to investigate light intensity and wavelength.

Work through any questions you missed again, then revise those areas before moving on to the next topic.