Photosynthesis MCQs With Answer: A focused study tool for B. Pharm students aiming to master plant bioenergetics, chlorophyll chemistry, and photochemical pathways. These targeted multiple-choice questions cover light-dependent reactions, the Calvin cycle, electron transport chains, ATP/NADPH synthesis, photophosphorylation, RuBisCO kinetics, C3/C4/CAM differences, and herbicide modes of action. Each item emphasizes biochemical mechanisms, chloroplast ultrastructure, pigment interactions, and pharmacologically relevant inhibitors of photosynthesis. Ideal for exam preparation, active revision, and improving problem-solving skills, this set reinforces core concepts vital to pharmaceutical sciences and research applications. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which pigment is the primary reaction-center chlorophyll in photosynthesis?
- Chlorophyll b
- Chlorophyll a
- Carotene
- Xanthophyll
Correct Answer: Chlorophyll a
Q2. In which chloroplast compartment does the Calvin cycle occur?
- Thylakoid lumen
- Thylakoid membrane
- Intermembrane space
- Stroma
Correct Answer: Stroma
Q3. Where do the light-dependent reactions of photosynthesis take place?
- Stroma
- Thylakoid membrane
- Chloroplast envelope
- Matrix
Correct Answer: Thylakoid membrane
Q4. What is the designation of the primary electron donor in Photosystem I?
- P680
- P700
- Chlorophyll b
- P870
Correct Answer: P700
Q5. Which pigment-protein complex is the primary reaction center of Photosystem II?
- P700
- P680
- Plastocyanin
- Ferredoxin
Correct Answer: P680
Q6. Which molecule is oxidized during water-splitting (photolysis) at PSII?
- NADP+
- Water
- Plastoquinone
- Oxygen
Correct Answer: Water
Q7. Which type of photophosphorylation generates both ATP and NADPH?
- Cyclic photophosphorylation
- Oxidative phosphorylation
- Substrate-level phosphorylation
- Non-cyclic photophosphorylation
Correct Answer: Non-cyclic photophosphorylation
Q8. Cyclic electron flow around PSI primarily produces which product?
- Oxygen
- NADPH
- ATP
- Carbon dioxide
Correct Answer: ATP
Q9. Which enzyme catalyzes the primary carboxylation step in the Calvin cycle?
- Phosphoglycerate kinase
- RuBisCO
- Ribulose-5-phosphate epimerase
- Triose phosphate isomerase
Correct Answer: RuBisCO
Q10. What is the immediate three-carbon product exported from the Calvin cycle that contributes to sugar synthesis?
- 3-Phosphoglycerate (3-PGA)
- Fructose-6-phosphate
- Glyceraldehyde-3-phosphate (G3P)
- Ribulose-1,5-bisphosphate (RuBP)
Correct Answer: Glyceraldehyde-3-phosphate (G3P)
Q11. How many CO2 molecules must be fixed to produce one molecule of glyceraldehyde-3-phosphate (G3P) in the Calvin cycle?
- 1
- 2
- 3
- 6
Correct Answer: 3
Q12. What is the primary electron acceptor in Photosystem II immediately after chlorophyll excitation?
- Pheophytin
- Plastoquinone
- Ferredoxin
- Plastocyanin
Correct Answer: Pheophytin
Q13. Which mobile carrier transfers electrons from PSII to the cytochrome b6f complex?
- Plastocyanin
- Ferredoxin
- Plastoquinone
- NADP+
Correct Answer: Plastoquinone
Q14. Which small copper-containing protein shuttles electrons from cytochrome b6f to PSI?
- Ferredoxin
- Plastocyanin
- Cytochrome c
- Ubiquinone
Correct Answer: Plastocyanin
Q15. What is the final electron acceptor in the noncyclic electron transport chain of photosynthesis?
- Oxygen
- ATP
- NADP+
- Water
Correct Answer: NADP+
Q16. During active photosynthesis where is the proton concentration highest?
- Chloroplast stroma
- Thylakoid lumen
- Intermembrane space
- Cytosol
Correct Answer: Thylakoid lumen
Q17. Which enzyme complex synthesizes ATP in chloroplasts?
- ATP synthase (CF0–CF1)
- RuBisCO
- Phosphofructokinase
- ATPase of mitochondria
Correct Answer: ATP synthase (CF0–CF1)
Q18. Which enzyme performs initial CO2 fixation in C4 plants in mesophyll cells?
- RuBisCO
- Carbonic anhydrase
- PEP carboxylase
- Malate dehydrogenase
Correct Answer: PEP carboxylase
Q19. CAM plants characteristically fix CO2 at which time to reduce water loss?
- Daytime
- Nighttime
- Dawn only
- Dusk only
Correct Answer: Nighttime
Q20. Which environmental condition increases the rate of photorespiration?
- Low oxygen concentration
- Low temperature
- High O2 concentration and high temperature
- High CO2 concentration
Correct Answer: High O2 concentration and high temperature
Q21. The herbicide DCMU (Diuron) inhibits photosynthesis by blocking electron transfer between which components?
- PSI and ferredoxin
- PSII and plastoquinone (QB site)
- Plastocyanin and PSI
- Cytochrome b6f and plastocyanin
Correct Answer: PSII and plastoquinone (QB site)
Q22. The Hill reaction demonstrates which measurable process in isolated chloroplasts?
- CO2 uptake
- O2 evolution using artificial electron acceptors
- ATP synthesis without light
- Protein synthesis
Correct Answer: O2 evolution using artificial electron acceptors
Q23. Which class of pigments provides photoprotection by quenching singlet oxygen and excess energy?
- Chlorophyll a
- Chlorophyll b
- Carotenoids
- Anthocyanins
Correct Answer: Carotenoids
Q24. What is the primary functional role of chlorophyll b in photosystems?
- Direct CO2 fixation
- Electron transport carrier
- Accessory pigment transferring energy to chlorophyll a
- Proton pumping
Correct Answer: Accessory pigment transferring energy to chlorophyll a
Q25. Quantum requirement in photosynthesis is best defined as which of the following?
- The number of CO2 molecules fixed per ATP used
- The number of photons required to evolve one molecule of O2
- The number of chlorophyll molecules per photosystem
- The number of electrons transported per photon
Correct Answer: The number of photons required to evolve one molecule of O2
Q26. The Z-scheme diagram represents which concept in photosynthesis?
- Pathway of carbon fixation in the Calvin cycle
- Redox potential changes showing electron flow from water to NADP+
- Sequence of chlorophyll biosynthesis steps
- Transportation of sugars to phloem
Correct Answer: Redox potential changes showing electron flow from water to NADP+
Q27. Which organelle contains the internal thylakoid membranes where light harvesting occurs?
- Mitochondrion
- Chloroplast
- Golgi apparatus
- Endoplasmic reticulum
Correct Answer: Chloroplast
Q28. Which structure provides the large surface area for light absorption in chloroplasts?
- Envelope membranes
- Stroma lamellae and stacked thylakoids (grana)
- Chromatin
- Matrix granules
Correct Answer: Stroma lamellae and stacked thylakoids (grana)
Q29. Classic isotope experiments (using 18O) established that oxygen produced in photosynthesis originates from which molecule?
- Carbon dioxide
- Water
- Atmospheric O2
- Glucose
Correct Answer: Water
Q30. Which protein is considered the most abundant enzyme on Earth and plays a central role in CO2 fixation?
- ATP synthase
- RuBisCO
- PEP carboxylase
- Nitrate reductase
Correct Answer: RuBisCO
Q31. In the Calvin cycle, NADPH is primarily used in which step?
- Carboxylation of RuBP
- Reduction of 3-phosphoglycerate to glyceraldehyde-3-phosphate
- Regeneration of RuBP
- Splitting of water
Correct Answer: Reduction of 3-phosphoglycerate to glyceraldehyde-3-phosphate
Q32. Which triose phosphate is the immediate export product from chloroplasts to the cytosol for sucrose synthesis?
- Fructose-1,6-bisphosphate
- Triose phosphate (G3P)
- Glucose-6-phosphate
- Ribulose-5-phosphate
Correct Answer: Triose phosphate (G3P)
Q33. The internal membrane system in chloroplasts responsible for light reactions is called what?
- Cristae
- Thylakoids
- Golgi cisternae
- Plasma membrane
Correct Answer: Thylakoids
Q34. Which wavelength region corresponds to the absorption maximum of chlorophyll a in PSII?
- 480 nm
- 550 nm
- 680 nm
- 700 nm
Correct Answer: 680 nm
Q35. Which molecule acts as the soluble electron carrier that reduces NADP+ to NADPH?
- Ferredoxin (via ferredoxin-NADP+ reductase)
- Plastiquinone
- Plastocyanin
- Cytochrome b6f
Correct Answer: Ferredoxin (via ferredoxin-NADP+ reductase)
Q36. Which enzyme transfers electrons from reduced ferredoxin to NADP+ to form NADPH?
- NADP+ synthase
- Ferredoxin-NADP+ reductase (FNR)
- Glutathione reductase
- NADH dehydrogenase
Correct Answer: Ferredoxin-NADP+ reductase (FNR)
Q37. Upon illumination, how does the pH of the thylakoid lumen change relative to the stroma?
- Remains equal
- Becomes more alkaline than stroma
- Becomes more acidic than stroma
- Becomes neutral
Correct Answer: Becomes more acidic than stroma
Q38. What is the name of the alternative electron sink that reduces O2 in chloroplasts, helping to dissipate excess electrons?
- Calvin-Benson cycle
- Mehler reaction (water-water cycle)
- Krebs cycle
- Glycolysis
Correct Answer: Mehler reaction (water-water cycle)
Q39. Light-harvesting complexes primarily function to do which of the following?
- Fix CO2
- Transfer excitation energy to reaction centers
- Synthesize ATP directly
- Transport sugars
Correct Answer: Transfer excitation energy to reaction centers
Q40. Photoinhibition from excessive light commonly damages which PSII protein, necessitating turnover and repair?
- Rubisco large subunit
- D1 protein of PSII
- Ferredoxin
- ATP synthase beta subunit
Correct Answer: D1 protein of PSII
Q41. Atrazine, a commonly used herbicide, inhibits photosynthesis by blocking electron flow at which site?
- PSI reaction center
- QB binding site of PSII
- ATP synthase active site
- Calvin cycle carboxylation
Correct Answer: QB binding site of PSII
Q42. In C4 photosynthesis, which intermediate is typically transported to bundle sheath cells for CO2 release?
- Oxaloacetate or malate
- Glyceraldehyde-3-phosphate
- Ribulose-1,5-bisphosphate
- Glucose-6-phosphate
Correct Answer: Oxaloacetate or malate
Q43. Which oxidized chlorophyll species directly extracts electrons from water at PSII?
- P700+
- P680+
- Chlorophyll b+
- Plastocyanin+
Correct Answer: P680+
Q44. When light intensity is saturating, which factor commonly becomes limiting for the rate of photosynthesis?
- Light wavelength
- CO2 concentration
- Chlorophyll content
- Photon energy
Correct Answer: CO2 concentration
Q45. Which molecule is exported from chloroplasts and is the main carbon substrate for cytosolic sucrose synthesis?
- Starch
- Triose phosphate (G3P)
- ATP
- Ribulose-5-phosphate
Correct Answer: Triose phosphate (G3P)
Q46. NADPH used in the Calvin cycle is generated primarily by which process?
- Cyclic electron flow around PSI
- Noncyclic photophosphorylation
- Glycolysis
- Respiratory electron transport
Correct Answer: Noncyclic photophosphorylation
Q47. Which role do carotenoids play in the photosynthetic apparatus relevant to pharmaceuticals and oxidative stress?
- Direct ATP synthesis
- Photoprotection and antioxidant defense
- Carboxylation of RuBP
- Electron donation to NADP+
Correct Answer: Photoprotection and antioxidant defense
Q48. Which technique is commonly used to measure PSII efficiency via chlorophyll fluorescence?
- Gas chromatography
- Pulse-Amplitude Modulated (PAM) fluorometry
- Mass spectrometry
- Western blotting
Correct Answer: Pulse-Amplitude Modulated (PAM) fluorometry
Q49. In C4 plants, decarboxylation of transported C4 acids to release CO2 occurs mainly in which cells?
- Mesophyll cells
- Bundle sheath cells
- Guard cells
- Root hair cells
Correct Answer: Bundle sheath cells
Q50. What is the typical ATP:NADPH stoichiometry required for fixation of one molecule of CO2 in the Calvin cycle?
- 1 ATP : 1 NADPH
- 2 ATP : 3 NADPH
- 3 ATP : 2 NADPH
- 4 ATP : 1 NADPH
Correct Answer: 3 ATP : 2 NADPH
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com