☀️ Photosynthesis in Higher Plants – NEET 2025 Complete Notes (Easy Language)
🔑 Target Keywords:
photosynthesis in higher plants neet notes, light reaction and dark reaction neet, c3 and c4 cycle, Photosynthesis[note 1] is a system of biological processes by which photopigment-bearing autotrophic organisms, such as most plants, algae and cyanobacteria, convert light energy — typically from sunlight — into the chemical energy necessary to fuel their metabolism. The term photosynthesis usually refers to oxygenic photosynthesis, a process that releases oxygen as a byproduct of water splitting. Photosynthetic organisms store the converted chemical energy within the bonds of intracellular organic compounds (complex compounds containing carbon), typically carbohydrates like sugars (mainly glucose, fructose and sucrose), starches, phytoglycogen and cellulose. When needing to use this stored energy, an organism's cells then metabolize the organic compounds through cellular respiration. Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earth's atmosphere, and it supplies most of the biological energy necessary for complex life on Earth.[2] 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.
Teacher ne bola tha —
“Yeh chapter fast mat padho, samajh ke padho. Agar basics clear ho gaye, toh har question aap khud bana loge!”
Toh bhai, apne paas NCERT aur ek rough copy rakh lo, kyunki hum diagram ke saath likh ke samjhenge 🌱
🌞 1. What Is Photosynthesis?
Definition:
The process by which green plants synthesize food (glucose) from carbon dioxide and water using sunlight and chlorophyll.
Equation:
💡 Simple Words:
“Sunlight se glucose banta hai — aur oxygen free hoti hai.”
🍃 2. Where Does Photosynthesis Occur?
Main site: Chloroplast (especially in mesophyll cells of leaves)
🔹 Structure of Chloroplast:
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Grana: Stack of thylakoids → Light reaction hoti hai.
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Stroma: Fluid region → Dark reaction (Calvin cycle) hoti hai.
Chlorophyll pigments:
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Chlorophyll a (main pigment)
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Chlorophyll b, xanthophyll, carotenoids (accessory pigments)
💡 Trick: “All pigments help absorb light, but only chlorophyll a performs photochemical reaction.”
⚡ 3. The Two Stages of Photosynthesis
| Stage | Location | Reaction Type |
|---|---|---|
| Light Reaction | Thylakoid | Converts light → chemical energy (ATP, NADPH) |
| Dark Reaction | Stroma | Converts CO₂ → Glucose |
🌞 4. Light Reaction (Hill Reaction)
Light reaction is also called the Hill reaction.
It was discovered by Robert Hill (1937).
🔹 Steps:
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Photon Absorption – Light absorbed by chlorophyll.
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Water Splitting (Photolysis):
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ATP Formation (Photophosphorylation):
ADP + Pi → ATP -
NADPH Formation:
NADP⁺ + 2e⁻ + 2H⁺ → NADPH
💡 Result: Light energy is converted into ATP and NADPH, which are used in dark reactions.
⚙️ 5. Types of Photophosphorylation
| Type | Site | Description | Example |
|---|---|---|---|
| Cyclic | PSI only | Electron returns to same PS | Bacteria |
| Non-Cyclic | PSI & PSII | Electron does not return | Plants |
Mnemonic: “Cyclic = Cycle complete, Non-cyclic = Exit electron.”
🌿 6. Dark Reaction (Calvin Cycle)
💡 Discovered by Melvin Calvin (1957).
Occurs in the stroma of chloroplast and does not need light directly.
Phases of Calvin Cycle:
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Carboxylation:
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CO₂ combines with RuBP (5C compound)
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Forms 2 molecules of 3-PGA (3C)
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Reduction:
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ATP and NADPH reduce 3-PGA to form glucose precursors.
-
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Regeneration:
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RuBP is regenerated to continue the cycle.
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End Product: Glucose
Equation:
🌾 7. C₃ and C₄ Pathways
🔹 C₃ Plants:
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CO₂ fixation by enzyme RuBisCO
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1st product → 3-PGA (3-carbon)
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Example: Wheat, Rice, Beans
🔹 C₄ Plants:
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CO₂ fixation by enzyme PEP Carboxylase
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1st product → Oxaloacetic acid (4-carbon)
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Example: Maize, Sugarcane, Sorghum
💡 Key Point:
C₄ plants avoid photorespiration → Higher productivity
🌱 8. Photorespiration – The Wasteful Process
Occurs when RuBisCO fixes O₂ instead of CO₂.
👉 Common in C₃ plants at high temperature.
No ATP or glucose formed – only energy loss.
💡 Trick:
Photorespiration = Photosynthesis reversed.
🌼 9. Factors Affecting Photosynthesis
| Factor | Description | Example |
|---|---|---|
| Light Intensity | Increases rate up to a limit | More sunlight → more glucose |
| CO₂ Concentration | Rate increases up to 0.04% | Beyond that, toxic |
| Temperature | Optimum 25–35°C | High temp = enzyme denaturation |
| Water | Required for photolysis | Lack = stomata close |
📚 10. NEET PYQs (2019–2024)
| Year | Question | Answer |
|---|---|---|
| 2020 | Site of light reaction? | Grana |
| 2021 | Enzyme in C₄ cycle? | PEP Carboxylase |
| 2022 | Photorespiration occurs in? | C₃ plants |
| 2023 | Product of photolysis? | Oxygen |
🧠 Smart Revision Tips
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Learn all enzyme names – RuBisCO, PEPcase, ATP synthase.
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Draw one chloroplast diagram daily.
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Practice Calvin cycle steps in sequence.
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Revise difference between C₃ and C₄ plants.
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Solve all PYQs on energy flow and photophosphorylation.
🔗 Related Blogs
🏁 Conclusion
Photosynthesis chapter aapke NEET syllabus ka core concept hai.
Agar aapne Light Reaction, Calvin Cycle, aur C₃–C₄ pathways ache se samajh liye, toh NEET 2025 me 4 marks fix hain 🔥
“Just like plants convert light into energy, a good student converts time into success.” 🌱