Calvin cycle and carbon fixation — practice questions

Question 1 · difficulty L1 · recall

Which five-carbon compound accepts carbon dioxide at the start of the Calvin cycle?

• A. RuBP
• B. PEP, the primary acceptor used in C4 mesophyll cells
• C. OAA
• D. PGA

Question 2 · difficulty L2 · understanding

What is the role of RuBisCO during the carboxylation phase of the Calvin cycle?

• A. It splits water to release oxygen
• B. Carboxylation of RuBP
• C. It transfers electrons from Photosystem I to NADP+
• D. It converts pyruvate directly into glucose

Question 3 · difficulty L2 · understanding

Why must RuBP be regenerated during the Calvin cycle?

• A. It provides oxygen for photorespiration
• B. It is the final carbohydrate exported from the chloroplast
• C. It regenerates the CO2 acceptor RuBP
• D. It acts as the reaction centre of Photosystem I

Question 4 · difficulty L3 · application

Three molecules of carbon dioxide enter the Calvin cycle. How many net molecules of triose phosphate are produced after allowing for RuBP regeneration?

• A. Six
• B. Two
• C. Three
• D. One

Question 5 · difficulty L3 · understanding

How many ATP and NADPH molecules are required to make one molecule of glucose through the Calvin pathway?

• A. 18 ATP and 12 NADPH
• B. 12 ATP and 18 NADPH
• C. 24 ATP and 18 NADPH
• D. 6 ATP and 12 NADPH

Question 6 · difficulty L3 · understanding

How many molecules of ATP and NADPH are required for every molecule of $$\mathrm{CO}_2$$ fixed in the Calvin cycle?

• A. 2 molecules of ATP and 3 molecules of NADPH
• B. 2 molecules of ATP and 2 molecules of NADPH
• C. 3 molecules of ATP and 3 molecules of NADPH
• D. 3 molecules of ATP and 2 molecules of NADPH

Question 7 · difficulty L3 · understanding

Which of the following are required for the dark reaction of photosynthesis? A. Light B. Chlorophyll C. $$\mathrm{CO}_2$$ D. ATP E. NADPH Choose the correct answer from the options given below:

• A. A, B and C only
• B. B, C and D only
• C. C, D and E only
• D. D and E only

Question 8 · difficulty L3 · understanding

How many ATP and NADPH 2 are required for the synthesis of one molecule of Glucose during Calvin cycle?

• A. 18 ATP and 12 NADPH 2
• B. 12 ATP and 16 NADPH 2
• C. 18 ATP and 16 NADPH 2
• D. 12 ATP and 12 NADPH 2

Question 9 · difficulty L4 · analysis

A chloroplast has abundant ATP but cannot generate NADPH. Which phase of the Calvin cycle would be most directly blocked?

• A. Reduction to triose phosphate
• B. Initial binding of carbon dioxide to RuBP
• C. Formation of oxygen from water
• D. Conversion of PEP to oxaloacetate

Question 10 · difficulty L5 · analysis

To obtain one molecule of glucose from six carbon dioxide molecules through the Calvin cycle, what total requirement is expected for ATP and NADPH?

• A. 12 ATP and 18 NADPH for six carbon dioxide molecules
• B. 18 ATP and 12 NADPH
• C. 6 ATP and 6 NADPH
• D. 24 ATP and 6 NADPH