Biology - Chapter 11: Photosynthesis in Higher Plants
Light Reaction, Calvin Cycle (C3), and Hatch-Slack Pathway (C4)
1. Overview of Photosynthesis
Photosynthesis is a physico-chemical process by which plants use sunlight to synthesize glucose from CO₂ and water.
| Reaction | Location | Products |
|---|---|---|
| Light Reaction | Grana (Thylakoids) | ATP, NADPH, O₂ |
| Dark Reaction (Calvin Cycle) | Stroma | Glucose (Sugar) |
💡 Quick Concept:
Light Reaction → Energy production
Dark Reaction → Food (Glucose) formation
2. Important Questions & Answers
Q1. Why is chlorophyll 'a' called the chief pigment?
Answer: Chlorophyll 'a' directly participates in converting light energy into chemical energy.
Other pigments act as accessory pigments and transfer energy to chlorophyll 'a'.
Q2. What is the Z-scheme in photosynthesis?
Answer: It represents the flow of electrons through PS II and PS I in a zig-zag pattern.
It involves photolysis of water and produces ATP, NADPH, and O₂.
Z-Scheme of Light Reaction
Q3. Explain the three stages of Calvin Cycle (C3 cycle).
Answer:
• Carboxylation → CO₂ fixation by RuBP
• Reduction → Formation of glucose using ATP & NADPH
• Regeneration → RuBP regenerated
• Carboxylation → CO₂ fixation by RuBP
• Reduction → Formation of glucose using ATP & NADPH
• Regeneration → RuBP regenerated
Q4. What is Kranz anatomy in C4 plants?
Answer: In C4 plants, bundle sheath cells surround vascular bundles.
This structure reduces photorespiration and increases efficiency in high temperature.
Q5. Why is photorespiration considered wasteful?
Answer: It does not produce ATP or glucose and instead consumes energy and releases CO₂.
Q6. What is Blackman’s Law of Limiting Factors?
Answer: The rate of a process is limited by the factor present in the least amount.
🔥 Exam Booster:
C3 → Normal plants
C4 → High efficiency plants
Photorespiration → Loss of energy