Photosynthesis in higher plants class 11 one shot | All concepts & Theory | Half NEET | By BHS Sir

☀️ 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, photophosphorylation

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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.

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 🌱

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🌞 1. What Is Photosynthesis?

Definition:

The process by which green plants synthesize food (glucose) from carbon dioxide and water using sunlight and chlorophyll.

Equation:

$$6CO_2 + 12H_2O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_6H_{12}O_6 + 6O_2 + 6H_2O$$

💡 Simple Words:
“Sunlight se glucose banta hai — aur oxygen free hoti hai.”

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🍃 2. Where Does Photosynthesis Occur?

Main site: Chloroplast (especially in mesophyll cells of leaves)

🔹 Structure of Chloroplast:

• Grana: Stack of thylakoids → Light reaction hoti hai.

• Stroma: Fluid region → Dark reaction (Calvin cycle) hoti hai.

Chlorophyll pigments:

• Chlorophyll a (main pigment)

• Chlorophyll b, xanthophyll, carotenoids (accessory pigments)

💡 Trick: “All pigments help absorb light, but only chlorophyll a performs photochemical reaction.”

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⚡ 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

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🌞 4. Light Reaction (Hill Reaction)

Light reaction is also called the Hill reaction.
It was discovered by Robert Hill (1937).

🔹 Steps:

1. Photon Absorption – Light absorbed by chlorophyll.

2. Water Splitting (Photolysis):

   $$2H_2O → 4H^+ + 4e^- + O_2$$

3. ATP Formation (Photophosphorylation):
   ADP + Pi → ATP

4. NADPH Formation:
   NADP⁺ + 2e⁻ + 2H⁺ → NADPH

💡 Result: Light energy is converted into ATP and NADPH, which are used in dark reactions.

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⚙️ 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.”

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🌿 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:

1. Carboxylation:

   • CO₂ combines with RuBP (5C compound)

   • Forms 2 molecules of 3-PGA (3C)

2. Reduction:

   • ATP and NADPH reduce 3-PGA to form glucose precursors.

3. Regeneration:

   • RuBP is regenerated to continue the cycle.

End Product: Glucose

Equation:

$$6CO_2 + 18ATP + 12NADPH → Glucose + 18ADP + 12NADP^+$$

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🌾 7. C₃ and C₄ Pathways

🔹 C₃ Plants:

• CO₂ fixation by enzyme RuBisCO

• 1st product → 3-PGA (3-carbon)

• Example: Wheat, Rice, Beans

🔹 C₄ Plants:

• CO₂ fixation by enzyme PEP Carboxylase

• 1st product → Oxaloacetic acid (4-carbon)

• Example: Maize, Sugarcane, Sorghum

💡 Key Point:
C₄ plants avoid photorespiration → Higher productivity

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🌱 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.

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🌼 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

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📚 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

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🧠 Smart Revision Tips

1. Learn all enzyme names – RuBisCO, PEPcase, ATP synthase.

2. Draw one chloroplast diagram daily.

3. Practice Calvin cycle steps in sequence.

4. Revise difference between C₃ and C₄ plants.

5. Solve all PYQs on energy flow and photophosphorylation.

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🔗 Related Blogs

• 🌿 Plant Physiology – Day 40

• 🍃 Respiration in Plants – Day 52

• ☀️ Mineral Nutrition – Day 41

• 🌾 Transpiration & Water Movement – Day 24

• 📚 NCERT Botany Smart Notes – Day 45

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🏁 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.” 🌱