🌞 Photosynthesis in Higher Plants – NEET 2025 Complete Notes
🔑 Target Keywords:
photosynthesis in higher plants neet notes, light reaction and dark reaction neet, c3 and c4 cycle, photophosphorylation, photosynthetic pigments neet
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🌱 Introduction – Let’s Start the Light Reaction!
Good evening, NEET aspirants 👋
Aaj hum start kar rahe hain ek high-weightage and concept-based chapter – Photosynthesis in Higher Plants.
Is chapter ka main aim hai: "Kaise plants light energy ko chemical energy me convert karte hain?"
Ye process sirf energy conversion nahi, balki life on Earth ka foundation hai 🌍💚
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☀️ 1. What Is Photosynthesis?
Definition (NCERT-based):
> “Photosynthesis is the process by which green plants synthesize organic food (glucose) from carbon dioxide and water in the presence of sunlight and chlorophyll.”
Equation:
6CO_2 + 12H_2O → C_6H_{12}O_6 + 6O_2 + 6H_2O
👉 Simple words me:
Plant sunlight, water aur carbon dioxide se glucose banata hai, aur byproduct me oxygen deta hai.
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🍃 2. Historical Background of Photosynthesis
Scientist Contribution
Joseph Priestley (1774) Discovered oxygen released by plants.
Jan Ingenhousz (1779) Showed that sunlight is essential.
Julius von Sachs (1854) Found that chlorophyll is necessary.
T.W. Engelmann (1888) Discovered action spectrum using Cladophora & bacteria.
💡 Trick to remember:
P-I-S-E → Priestley, Ingenhousz, Sachs, Engelmann
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🌿 3. Where Does Photosynthesis Occur?
Site: Chloroplast (in mesophyll cells of leaves)
Each chloroplast has:
Grana: Site of light reaction
Stroma: Site of dark reaction (Calvin cycle)
Structure Summary:
Double membrane organelle
Contains chlorophyll a & b
Thylakoids arranged as stacks (grana)
Stroma has enzymes for CO₂ fixation
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🌈 4. Pigments Involved in Photosynthesis
Photosynthesis me pigments sunlight absorb karte hain.
Pigment Colour Function
Chlorophyll a Blue-green Main pigment (reaction center)
Chlorophyll b Yellow-green Accessory pigment
Xanthophylls Yellow Protects from photooxidation
Carotenoids Orange Accessory pigment
📊 Action Spectrum (Engelmann experiment):
Maximum photosynthesis occurs in blue & red light.
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⚡ 5. Mechanism of Photosynthesis
Photosynthesis hota hai 2 steps me:
1. Light Reaction (Hill Reaction) – in Grana
2. Dark Reaction (Calvin Cycle) – in Stroma
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☀️ (A) Light Reaction (Photochemical Phase)
Site: Thylakoid membrane
Main Events:
Light absorption by chlorophyll
Excitation of electrons
Splitting of water (Photolysis)
ATP and NADPH formation (Photophosphorylation)
Equation:
2H_2O → 4H^+ + O_2 + 4e^-
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💥 Photophosphorylation Types
Type Site Product Notes
Non-Cyclic Both Photosystems (I & II) ATP + NADPH + O₂ Major pathway
Cyclic Photosystem I only ATP only Occurs when NADP⁺ not available
💡 Trick:
Non-Cyclic = Normal, Cyclic = Compensation
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🌿 6. Dark Reaction (Biosynthetic Phase / Calvin Cycle)
Site: Stroma
Scientist: Melvin Calvin (used radioactive Carbon-14)
Steps:
1. Carboxylation: CO₂ fixed by RuBisCO → 3-PGA
2. Reduction: ATP & NADPH used → 3-PGA → PGAL
3. Regeneration: RuBP regenerated using ATP
Net Result:
6CO₂ → 1 Glucose molecule
💡 Remember: Light reaction gives ATP + NADPH used in dark reaction.
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🌾 7. C₃ and C₄ Pathways
🔹 C₃ Cycle (Calvin Cycle)
First stable product: 3-PGA (3-carbon)
Enzyme: RuBisCO
Occurs in: Rice, Wheat, Potato
Disadvantage: Photorespiration occurs
🔹 C₄ Cycle (Hatch and Slack Pathway)
First stable product: OAA (4-carbon)
Occurs in: Maize, Sugarcane
Advantage: No photorespiration
Specialized anatomy: Kranz Anatomy (bundle sheath cells)
💡 Trick:
“C₃ = Cool plants, C₄ = Hot plants”
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🌵 8. CAM Pathway (Crassulacean Acid Metabolism)
Occurs in succulents like Opuntia, Pineapple
Stomata open at night → CO₂ fixed as malic acid
Stomata close at day → CO₂ used for Calvin cycle
👉 Adaptation to desert conditions
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🌞 9. Factors Affecting Photosynthesis
Factor Effect
Light intensity Increases rate up to saturation
CO₂ concentration Limiting factor
Temperature Optimum 25–35°C
Water Indirectly affects (wilting closes stomata)
💡 Law of Limiting Factor (Blackman’s Law):
“When several factors affect a process, the slowest one limits the rate.”
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🧠 10. NEET PYQs (2018–2024)
Year Question Answer
2020 Kranz anatomy found in? C₄ plants
2021 Which pigment acts as reaction center? Chlorophyll a
2022 Which step needs RuBisCO? Carboxylation
2023 In C₄ plants, Calvin cycle occurs in? Bundle sheath cells
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📚 11. Quick Revision Table
Feature C₃ Plants C₄ Plants
First Product 3-PGA OAA
Photorespiration Present Absent
Enzyme RuBisCO PEP + RuBisCO
Anatomy Normal Kranz
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🎯 12. NEET Strategy
1. Learn all diagrams (Z-scheme, Calvin Cycle, Kranz Anatomy)
2. Focus on pigments + enzymes + locations
3. Revise PYQs (2015–2024)
4. Practice numerical on quantum yield
5. Understand light & dark reaction link
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🔗 Related Blogs
🌿 Respiration in Plants – Day 51
🍃 Plant Growth & Development – Day 52
🌸 Morphology of Flowering Plants – Day 5
🌱 Anatomy of Flowering Plants – Day 49
☀️ Mineral Nutrition – Day 20
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🏁 Conclusion
Photosynthesis in Higher Plants ek concept + diagram + equation-based chapter hai.
Agar aap Light reaction + Calvin Cycle + C₄ pathway acche se kar lete ho, toh 12–16 marks guaranteed hain!
So, open your NCERT, focus on every line, and keep revising with your Botany Sir 🌿💪