photosynthesis in higher plants class 11 notes neet pdf | NEET 2026 | By BHS sir

🌞 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

---

🌱 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 🌍💚

---

☀️ 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.

---

🍃 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

---

🌿 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

---

🌈 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.

---

⚡ 5. Mechanism of Photosynthesis

Photosynthesis hota hai 2 steps me:

1. Light Reaction (Hill Reaction) – in Grana

2. Dark Reaction (Calvin Cycle) – in Stroma

---

☀️ (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^-

---

💥 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

---

🌿 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.

---

🌾 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”

---

🌵 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

---

🌞 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.”

---

🧠 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

---

📚 11. Quick Revision Table

Feature C₃ Plants C₄ Plants

First Product 3-PGA OAA

Photorespiration Present Absent

Enzyme RuBisCO PEP + RuBisCO

Anatomy Normal Kranz

---

🎯 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

---

🔗 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

---

🏁 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 🌿💪