Level 1 — RecognitionPhotosynthesis

Photosynthesis

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1: Recognition

Time limit: 20 minutes Total marks: 30

Section A — Multiple Choice (1 mark each)

Choose the single best answer.

Q1. The overall balanced equation for photosynthesis is:

A) $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$
B) $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$
C) $6CO_2 + 12H_2O \rightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O$
D) $6O_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6CO_2$

Q2. The light-dependent reactions occur in the:

A) Stroma
B) Thylakoid membranes
C) Outer chloroplast membrane
D) Cytoplasm

Q3. The main photosynthetic pigment that absorbs mostly red and blue light is:

A) Chlorophyll a
B) Xanthophyll
C) Carotene
D) Phycocyanin

Q4. Photolysis of water directly produces all of the following EXCEPT:

A) Oxygen
B) Protons ( $H^+$ )
C) Electrons
D) Glucose

Q5. The primary product of carbon fixation in the Calvin cycle (first stable compound) is:

A) Glucose
B) 3-phosphoglycerate (3-PGA / GP)
C) RuBP
D) Oxaloacetate

Q6. The enzyme RuBisCO catalyses the reaction between $CO_2$ and:

A) 3-PGA
B) Ribulose bisphosphate (RuBP)
C) Glucose
D) PEP

Q7. Cyclic photophosphorylation produces:

A) ATP only
B) NADPH only
C) ATP and NADPH
D) Oxygen only

Q8. In C4 plants, the initial $CO_2$ acceptor is:

A) RuBP
B) Phosphoenolpyruvate (PEP)
C) Glucose
D) NADP⁺

Q9. Photorespiration occurs when RuBisCO fixes:

A) $CO_2$
B) $O_2$
C) $H_2O$
D) $N_2$

Q10. Which is NOT normally a limiting factor of photosynthesis?

A) Light intensity
B) $CO_2$ concentration
C) Temperature
D) Oxygen concentration

Section B — Matching (1 mark each, 5 marks)

Q11. Match each structure/molecule (i–v) to its function (P–T).

Item		Function
i. Thylakoid		P. Site of Calvin cycle
ii. Stroma		Q. Splits water
iii. NADPH		R. Contains chlorophyll; light reactions
iv. Photosystem II		S. Reduced electron carrier from light reactions
v. RuBisCO		T. Fixes carbon dioxide

Section C — True/False with Justification (2 marks each: 1 T/F, 1 justification)

Q12. CAM plants open their stomata at night to fix $CO_2$ . (2)

Q13. Non-cyclic photophosphorylation produces both ATP and NADPH. (2)

Q14. Carotenoids absorb light and pass energy to chlorophyll, acting as accessory pigments. (2)

Q15. Photosynthesis releases $CO_2$ and consumes $O_2$ , exactly like respiration. (2)

Q16. In C4 plants, the Calvin cycle occurs in mesophyll cells. (2)

Q17. At low light intensity, light is the limiting factor of photosynthesis. (2)

Answer keyMark scheme & solutions

Q1 — A. $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$ is the standard overall summary equation. (Option C is the biochemically detailed version but not the "overall" summary requested.) (1)

Q2 — B. Light reactions occur on/in thylakoid membranes where photosystems and electron transport chains are embedded. (1)

Q3 — A. Chlorophyll a is the primary pigment; absorbs strongly in blue (~430 nm) and red (~660 nm), reflecting green. (1)

Q4 — D. Photolysis: $2H_2O \rightarrow 4H^+ + 4e^- + O_2$ . Glucose is a later Calvin-cycle product, not from photolysis. (1)

Q5 — B. $CO_2$ + RuBP → two molecules of 3-PGA (first stable product). (1)

Q6 — B. RuBisCO joins $CO_2$ to RuBP. (1)

Q7 — A. Cyclic flow around PSI regenerates ATP only (no water split, no NADPH). (1)

Q8 — B. PEP + $CO_2$ → oxaloacetate (4-carbon) in mesophyll of C4 plants. (1)

Q9 — B. RuBisCO's oxygenase activity fixes $O_2$ , initiating photorespiration. (1)

Q10 — D. Oxygen is a product, not typically a limiting factor (unlike light, $CO_2$ , temperature). (1)

Section B

Q11 (5 marks, 1 each):

i → R (Thylakoid contains chlorophyll, site of light reactions)
ii → P (Stroma, site of Calvin cycle)
iii → S (NADPH, reduced electron carrier)
iv → Q (PSII splits water/photolysis)
v → T (RuBisCO fixes $CO_2$ )

Section C (2 marks each: 1 T/F + 1 justification)

Q12 — TRUE (1). CAM plants (e.g. cacti) open stomata at night to reduce water loss; $CO_2$ is stored as malic acid and released for the Calvin cycle by day. (1 justification)

Q13 — TRUE (1). Non-cyclic (Z-scheme) uses PSII and PSI; water is split (giving $O_2$ ), ATP is made by chemiosmosis, and electrons reduce NADP⁺ to NADPH. (1)

Q14 — TRUE (1). Carotenoids capture wavelengths chlorophyll absorbs poorly and transfer energy to reaction-centre chlorophyll, broadening the usable spectrum. (1)

Q15 — FALSE (1). Photosynthesis consumes $CO_2$ and releases $O_2$ — the opposite of respiration. (1)

Q16 — FALSE (1). In C4 plants the Calvin cycle occurs in bundle-sheath cells; only initial $CO_2$ fixation (via PEP) is in mesophyll. (1)

Q17 — TRUE (1). At low light, rate rises with light intensity, so light is limiting; other factors are in excess. (1)

[
  {"claim":"Photosynthesis equation Q1 balances: 6CO2+6H2O -> C6H12O6+6O2 (C,H,O conserved)","code":"C_l=6; H_l=12; O_l=6*2+6*1; C_r=6; H_r=12; O_r=6+6*2; result=(C_l==C_r and H_l==H_r and O_l==O_r)"},
  {"claim":"Photolysis Q4: 2H2O -> 4H+ +4e- + O2 conserves H, O and charge","code":"H_l=4; O_l=2; H_r=4; O_r=2; charge_r=4*1+4*(-1); result=(H_l==H_r and O_l==O_r and charge_r==0)"},
  {"claim":"Calvin Q5: CO2(1C)+RuBP(5C) gives 6C splitting into two 3-carbon 3-PGA","code":"total_C=1+5; product=2*3; result=(total_C==product)"},
  {"claim":"C4 Q8: PEP(3C)+CO2(1C) yields oxaloacetate 4C","code":"result=(3+1==4)"}
]