Part 3 — Chemiosmosis, ATP/NADPH Utilization, Calvin Cycle (Q51–75)
Part 3 (Q51–75) of Chapter 13 – Photosynthesis in Higher Plants (Class 11, NEET relevance).
This section covers Chemiosmosis, ATP/NADPH Utilization, and the Calvin Cycle (C₃ pathway).
Part 3 — Chemiosmosis, ATP/NADPH Utilization, Calvin Cycle (Q51–75)
Q51.
The chemiosmotic hypothesis for ATP synthesis was proposed by:
A. Engelmann
B. Peter Mitchell ✅
C. Blackman
D. Calvin
Explanation:
- A. Discovered action spectrum.
- B. (Correct) Peter Mitchell proposed chemiosmotic theory (proton gradient drives ATP synthesis).
- C. Limiting factors law.
- D. Calvin cycle discovery.
Q52.
In chloroplast, protons accumulate in:
A. Stroma
B. Thylakoid lumen ✅
C. Cytoplasm
D. Outer membrane
Explanation:
- A. Lower proton concentration.
- B. (Correct) Proton gradient develops in thylakoid lumen.
- C/D. Not sites of accumulation.
Q53.
ATP synthesis in chloroplast occurs when:
A. Protons move into stroma through CF₀–CF₁ ATP synthase ✅
B. Protons accumulate in cytoplasm
C. NADP⁺ accepts electrons
D. CO₂ is fixed
Explanation:
- A. (Correct) Proton flow through ATP synthase drives phosphorylation of ADP → ATP.
- B–D. Related to other processes.
Q54.
Which provides reducing power for Calvin cycle?
A. ATP
B. NADPH ✅
C. Oxygen
D. PEP
Explanation:
- A. Provides energy, not reducing power.
- B. (Correct) NADPH provides electrons for CO₂ reduction.
- C/D. Not reducing agents in this context.
Q55.
How many ATP and NADPH are required for fixation of one molecule of CO₂ in Calvin cycle?
A. 1 ATP + 1 NADPH
B. 3 ATP + 2 NADPH ✅
C. 2 ATP + 2 NADPH
D. 2 ATP + 1 NADPH
Explanation:
- A/C/D. Incorrect ratios.
- B. (Correct) 3 ATP + 2 NADPH needed per CO₂ fixed.
Q56.
How many turns of Calvin cycle are required to produce one glucose molecule?
A. 3
B. 6 ✅
C. 12
D. 2
Explanation:
- A. 3 turns produce one G3P.
- B. (Correct) 6 turns fix 6 CO₂ → one glucose.
- C/D. Not correct.
Q57.
The primary CO₂ acceptor in Calvin cycle is:
A. Phosphoenolpyruvate (PEP)
B. Ribulose-1,5-bisphosphate (RuBP) ✅
C. Pyruvate
D. Glucose
Explanation:
- A. CO₂ acceptor in C₄ plants.
- B. (Correct) RuBP accepts CO₂, catalyzed by Rubisco.
- C/D. Not CO₂ acceptors.
Q58.
Which enzyme catalyzes the first step of Calvin cycle?
A. Rubisco ✅
B. PEP carboxylase
C. ATP synthase
D. Ferredoxin reductase
Explanation:
- A. (Correct) Rubisco catalyzes RuBP + CO₂ → 3-PGA.
- B. CO₂ fixation enzyme in C₄ plants.
- C/D. Not Calvin cycle enzymes.
Q59.
Rubisco enzyme is located in:
A. Thylakoid membrane
B. Stroma of chloroplast ✅
C. Cytoplasm
D. Mitochondria
Explanation:
- A. Light reaction location.
- B. (Correct) Rubisco resides in stroma → CO₂ fixation.
- C/D. Not correct.
Q60.
The Calvin cycle operates in:
A. Light only
B. Both light and dark ✅
C. Dark only
D. Absence of CO₂
Explanation:
- A. Misconception.
- B. (Correct) Calvin cycle requires ATP/NADPH from light reactions, but itself is light-independent → can occur in both if energy is available.
- C. Not true, “dark reaction” is misnomer.
- D. CO₂ is essential.
Q61.
How many molecules of 3-phosphoglyceric acid (3-PGA) are formed from fixation of 3 CO₂?
A. 2
B. 6 ✅
C. 3
D. 4
Explanation:
- A/C/D. Incorrect counts.
- B. (Correct) Each CO₂ → 2 PGA. Thus, 3 CO₂ → 6 PGA.
Q62.
Which phase of Calvin cycle consumes ATP but not NADPH?
A. Carboxylation
B. Reduction
C. Regeneration of RuBP ✅
D. All of these
Explanation:
- A. No energy consumed.
- B. Requires both ATP and NADPH.
- C. (Correct) RuBP regeneration requires only ATP.
- D. Not true.
Q63.
How many ATP and NADPH are needed for producing one molecule of glucose?
A. 6 ATP + 6 NADPH
B. 12 ATP + 12 NADPH
C. 18 ATP + 12 NADPH ✅
D. 24 ATP + 12 NADPH
Explanation:
- A/B/D. Incorrect counts.
- C. (Correct) 6 CO₂ → 18 ATP + 12 NADPH required for 1 glucose.
Q64.
Which molecule is considered the “CO₂ acceptor” and “regenerated” at the end of Calvin cycle?
A. PEP
B. RuBP ✅
C. Pyruvate
D. Malate
Explanation:
- A/D. C₄ cycle intermediates.
- B. (Correct) RuBP regenerated to continue cycle.
- C. Not involved.
Q65.
Which statement is true about the Calvin cycle?
A. ATP is produced in stroma
B. ATP is consumed in stroma ✅
C. It occurs in mitochondria
D. CO₂ is released
Explanation:
- A. ATP is produced in thylakoids.
- B. (Correct) ATP generated in light reaction is consumed in stroma for Calvin cycle.
- C/D. Not correct.
Q66.
Which compound is the first stable product of Calvin cycle?
A. G3P
B. 3-PGA ✅
C. OAA
D. RuBP
Explanation:
- A. G3P is produced later.
- B. (Correct) 3-phosphoglyceric acid is first stable product.
- C. OAA is first product of C₄.
- D. CO₂ acceptor, not product.
Q67.
The Calvin cycle is also known as:
A. C₂ cycle
B. Reductive pentose phosphate pathway ✅
C. Krebs cycle
D. Glycolysis
Explanation:
- A. C₂ = photorespiration.
- B. (Correct) Calvin cycle is reductive pentose phosphate cycle.
- C/D. Different pathways.
Q68.
The final product of Calvin cycle is:
A. ATP
B. Glyceraldehyde-3-phosphate (G3P) ✅
C. NADPH
D. RuBP
Explanation:
- A/C/D. Not product.
- B. (Correct) G3P is the output that can form glucose and other sugars.
Q69.
The ratio of ATP:NADPH used in Calvin cycle is:
A. 1:1
B. 2:3
C. 3:2 ✅
D. 1:2
Explanation:
- A/B/D. Not correct.
- C. (Correct) Calvin cycle consumes 3 ATP : 2 NADPH per CO₂ fixed.
Q70.
Which compound formed in Calvin cycle can directly enter glycolysis?
A. RuBP
B. G3P ✅
C. PGA
D. Malate
Explanation:
- A/C. Intermediates in cycle.
- B. (Correct) G3P can enter glycolysis or be used to form glucose, starch.
- D. C₄ intermediate.
Q71.
Which step in Calvin cycle fixes CO₂?
A. Carboxylation ✅
B. Reduction
C. Regeneration
D. All steps
Explanation:
- A. (Correct) Carboxylation: RuBP + CO₂ → 2 × 3-PGA.
- B/C. Later steps.
- D. Not true.
Q72.
Which enzyme catalyzes regeneration of RuBP?
A. Rubisco
B. Phosphoribulokinase ✅
C. PEP carboxylase
D. Ferredoxin
Explanation:
- A. Fixes CO₂.
- B. (Correct) Phosphoribulokinase regenerates RuBP using ATP.
- C/D. Not correct.
Q73.
The Calvin cycle was elucidated by:
A. Calvin and Benson ✅
B. Blackman
C. Mitchell
D. Priestley
Explanation:
- A. (Correct) Calvin & Benson traced C¹⁴-labeled CO₂ in algae → Calvin cycle.
- B–D. Different contributions.
Q74.
The product that directly exits Calvin cycle to form sugars is:
A. PGA
B. G3P ✅
C. RuBP
D. ATP
Explanation:
- A. Intermediate.
- B. (Correct) G3P exits cycle → forms glucose, starch, sucrose.
- C/D. Not products.
Q75.
Which statement about Calvin cycle is incorrect?
A. It requires ATP and NADPH
B. It produces glucose directly ✅
C. It fixes CO₂
D. It occurs in stroma
Explanation:
- A/C/D. Correct.
- B. (Correct) Calvin cycle produces G3P, not glucose directly.
Photosynthesis Class 11, Photosynthesis NEET MCQs, Light reaction Z scheme, Calvin cycle C3 pathway, C4 pathway Kranz anatomy, Photorespiration C2 cycle, Factors affecting photosynthesis, Class 11 Biology MCQs, photosynthesis in higher plants class 11 mcqs, light reaction and z scheme neet questions, calvin cycle c3 pathway notes ncert, c4 pathway and kranz anatomy neet, photorespiration c2 cycle class 11 biology, factors affecting photosynthesis neet questions, photosynthesis experiments class 11 solved mcqs, class 11 biology photosynthesis online learning for neet