The Calvin Cycle, also known as the Calvin-Benson cycle, is a series of biochemical reactions that occur in the stroma of chloroplasts during photosynthesis. It uses carbon dioxide, ATP, and NADPH to produce glucose and other carbohydrates. The cycle begins with the enzyme RuBisCO fixing carbon dioxide to ribulose bisphosphate (RuBP), forming an unstable 6-carbon compound that quickly splits into two molecules of 3-phosphoglycerate (3-PGA). Through a series of steps, ATP and NADPH are used to reduce 3-PGA into glyceraldehyde-3-phosphate (G3P), which can be used to form glucose. The cycle regenerates RuBP to continue the process. This Calvin Cycle MCQs with Answers will help you to learn the concept easily.
Plant Physiology Notes | Plant Physiology MCQs | Plant Physiology PPTs
1. What is the difference between cyclic and non-cyclic photophosphorylation?
a) Cyclic photophosphorylation produces ATP and NADPH, while non-cyclic only produces ATP.
b) Non-cyclic photophosphorylation uses both PSII and PSI, while cyclic uses only PSI.
c) Both produce equal amounts of ATP.
d) Both processes involve the same number of photosystems.
Answer: b) Non-cyclic photophosphorylation uses both PSII and PSI, while cyclic uses only PSI.
2. What is the primary role of ATP in photosynthesis?
a) To provide energy for splitting water molecules
b) To reduce NADP+ to NADPH
c) To provide energy for the Calvin cycle
d) To transport electrons across the thylakoid membrane
Answer: c) To provide energy for the Calvin cycle
3. Where does photophosphorylation take place?
a) In the stroma
b) In the thylakoid membranes
c) In the cytoplasm
d) In the mitochondria
Answer: b) In the thylakoid membranes
4. Which of the following is the starting molecule for the Calvin cycle?
a) Glucose
b) RuBP (Ribulose bisphosphate)
c) Oxygen
d) NADPH
Answer: b) RuBP (Ribulose bisphosphate)
5. Which enzyme catalyzes the first step of the Calvin cycle?
a) ATP synthase
b) Rubisco
c) NADP+ reductase
d) PEP carboxylase
Answer: b) Rubisco
6. What is produced at the end of the Calvin cycle?
a) Glucose
b) Oxygen
c) NADPH
d) G3P (Glyceraldehyde 3-phosphate)
Answer: d) G3P (Glyceraldehyde 3-phosphate)
7. How many molecules of G3P are needed to form one molecule of glucose?
a) 1
b) 2
c) 3
d) 6
Answer: b) 2
8. What happens to CO2 in the Calvin cycle?
a) It is split into oxygen and hydrogen
b) It is used to form glucose
c) It is reduced to form NADPH
d) It is oxidized to form oxygen
Answer: b) It is used to form glucose
9. Which molecule is directly involved in transferring light energy to chemical energy in photosynthesis?
a) Oxygen
b) Chlorophyll
c) Carbon dioxide
d) ATP
Answer: b) Chlorophyll
10. What role does ATP synthase play in photosynthesis?
a) It synthesizes NADPH
b) It splits water molecules
c) It converts light energy into ATP
d) It uses the proton gradient to produce ATP
Answer: d) It uses the proton gradient to produce ATP
11. What is the source of electrons for the light-dependent reactions of photosynthesis?
a) NADPH
b) Water molecules
c) Glucose
d) Oxygen
Answer: b) Water molecules
12. Which of the following is true about the Calvin cycle?
a) It occurs in the thylakoid membranes
b) It requires light to function
c) It uses ATP and NADPH to convert carbon dioxide into glucose
d) It produces oxygen as a by-product
Answer: c) It uses ATP and NADPH to convert carbon dioxide into glucose
13. Which of the following molecules is not part of the light-dependent reactions?
a) NADPH
b) Oxygen
c) ATP
d) Glucose
Answer: d) Glucose
14. How does the energy in sunlight ultimately benefit the plant?
a) It is stored in glucose
b) It is used to warm the plant
c) It helps the plant grow roots
d) It is used for cellular respiration
Answer: a) It is stored in glucose
15. What happens to the oxygen produced during the light-dependent reactions?
a) It is used in the Calvin cycle
b) It is released as a by-product
c) It is stored in chloroplasts
d) It is absorbed by plants
Answer: b) It is released as a by-product
16. Which photosystem is involved in producing NADPH?
a) PSI
b) PSII
c) Both PSI and PSII
d) Neither PSI nor PSII
Answer: a) PSI
17. What is the function of the proton gradient in photosynthesis?
a) To synthesize glucose
b) To reduce NADP+
c) To drive ATP synthesis
d) To release oxygen
Answer: c) To drive ATP synthesis
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