CBSE Class 11 Biology – Photosynthesis in Higher Plants | Case-Based / Source-Based Questions with Answers (NCERT Based)

Course & Examination Details

Course: CBSE Class 11 Biology
Unit: Unit IV – Plant Physiology
Chapter: Chapter 13 – Photosynthesis in Higher Plants
Prescribed Textbook: NCERT
Board: CBSE

CBSE Board Examination Context

• Case-based questions test concept application, analysis, and reasoning
• Fully aligned with competency-based assessment pattern
• Answers are precise, NCERT-specific, and exam-oriented

Section A: Light Reaction (Case-Based Questions 1–8)

Case 1

A leaf exposed to sunlight releases oxygen even when carbon dioxide is absent.

Q1. Which phase of photosynthesis is responsible for oxygen release?
Ans: Oxygen is released during the light reaction due to photolysis of water.

Case 2

An experiment shows splitting of water molecules in chloroplasts under light.

Q2. Name the process responsible for this observation.
Ans: The process is photolysis of water occurring in Photosystem II.

Case 3

A student observes that ATP and NADPH are formed only in presence of light.

Q3. Identify the phase of photosynthesis involved.
Ans: The light-dependent reaction is responsible for ATP and NADPH formation.

Case 4

Electron flow in a chloroplast produces ATP but no NADPH or oxygen.

Q4. Which type of photophosphorylation is occurring?
Ans: Cyclic photophosphorylation is occurring.

Case 5

A mutant plant lacks Photosystem II.

Q5. Which product of photosynthesis will be absent?
Ans: Oxygen will be absent as photolysis of water occurs in Photosystem II.

Case 6

An increase in proton concentration is observed inside thylakoids.

Q6. Which process uses this gradient to produce ATP?
Ans: Chemiosmosis uses the proton gradient to synthesize ATP.

Case 7

A plant exposed to intense light shows photo-oxidation damage.

Q7. Which pigments protect chlorophyll from such damage?
Ans: Carotenoids protect chlorophyll from photo-oxidation.

Case 8

ATP synthesis continues even when NADP⁺ becomes limiting.

Q8. Which pathway supports ATP synthesis in this condition?
Ans: Cyclic photophosphorylation supports ATP synthesis.

Section B: Dark Reaction / Calvin Cycle (Case-Based Questions 9–14)

Case 9

Carbon dioxide fixation occurs even in absence of light but stops when ATP is exhausted.

Q9. Name the reaction involved.
Ans: The dark reaction or Calvin cycle is involved.

Case 10

A chloroplast enzyme fixes CO₂ but also reacts with oxygen.

Q10. Identify the enzyme.
Ans: RuBisCO is the enzyme showing both carboxylase and oxygenase activity.

Case 11

A decrease in sugar formation is observed at high temperature in C₃ plants.

Q11. Which process causes this reduction?
Ans: Photorespiration causes reduced sugar formation.

Case 12

ATP and NADPH are supplied externally to a chloroplast preparation.

Q12. Will CO₂ fixation occur? Give reason.
Ans: Yes, because Calvin cycle requires ATP and NADPH, not light directly.

Case 13

A leaf shows reduced photosynthesis when RuBP regeneration is affected.

Q13. Which phase of Calvin cycle is disturbed?
Ans: The regeneration phase of the Calvin cycle is disturbed.

Case 14

A plant shows increased photosynthesis under high CO₂ concentration.

Q14. Which step of Calvin cycle is enhanced?
Ans: Carboxylation step is enhanced due to increased CO₂ availability.

Section C: C₃ and C₄ Pathways (Case-Based Questions 15–20)

Case 15

A plant shows photorespiration under high temperature.

Q15. Identify the type of plant.
Ans: It is a C₃ plant.

Case 16

A plant exhibits Kranz anatomy and high productivity.

Q16. Identify the photosynthetic pathway.
Ans: The plant follows the C₄ pathway.

Case 17

CO₂ fixation occurs initially in mesophyll cells forming a four-carbon compound.

Q17. Name the compound formed.
Ans: Oxaloacetic acid (OAA) is formed.

Case 18

RuBisCO is restricted to bundle sheath cells in a plant.

Q18. Name the plant type.
Ans: It is a C₄ plant.

Case 19

A plant requires extra ATP for carbon fixation but avoids photorespiration.

Q19. Which pathway does it follow?
Ans: The plant follows the C₄ pathway.

Case 20

A plant performs photosynthesis efficiently at high light and temperature.

Q20. Why is it advantageous ecologically?
Ans: C₄ plants avoid photorespiration and show higher efficiency in tropical conditions.

Section D: Factors Affecting Photosynthesis (Case-Based Questions 21–25)

Case 21

Photosynthesis rate remains low despite high light intensity.

Q21. Which factor may be limiting?
Ans: Carbon dioxide concentration may be the limiting factor.

Case 22

A plant shows reduced photosynthesis during drought.

Q22. What is the immediate cause?
Ans: Stomatal closure reduces CO₂ entry.

Case 23

An increase in temperature beyond optimum reduces photosynthesis.

Q23. Explain the reason.
Ans: High temperature denatures enzymes and increases photorespiration.

Case 24

A shaded plant shows lower photosynthetic rate.

Q24. Which factor is responsible?
Ans: Low light intensity limits photosynthesis.

Case 25

A plant is exposed to favourable light, CO₂, and temperature but still shows limited photosynthesis.

Q25. Which principle explains this?
Ans: Blackman’s law of limiting factors explains this observation.

Best Suited For

• CBSE Class 11 Annual Examinations
• Competency-based & case-study questions
• NCERT-aligned conceptual assessment