What is Photosynthesis?
Photosynthesis is the process by which green plants prepare their own food using sunlight, carbon dioxide, and water.
Chemical Equation
6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O
Photosynthesis occurs in the chloroplasts of green plant cells.
Why is Photosynthesis Important?
Primary source of food on Earth
Releases oxygen into the atmosphere
Maintains carbon dioxide balance
Converts solar energy into chemical energy
Supports all ecosystems
Factors Necessary for Photosynthesis
External Factors
Light
Carbon dioxide
Water
Temperature
Internal Factors
Chlorophyll content
Leaf anatomy
Protoplasmic condition
Enzyme activity
Site of Photosynthesis
Photosynthesis occurs in the chloroplast.
Structure of Chloroplast
Outer membrane
Inner membrane
Stroma
Grana
Thylakoids
NCERT Point
Grana contain chlorophyll pigments and are the site of light reactions.
Photosynthetic Pigments
Chlorophyll a
Primary pigment
Blue-green color
Reaction center pigment
Chlorophyll b
Accessory pigment
Yellow-green color
Carotenoids
Carotenes
Xanthophylls
NCERT Important Line
Chlorophyll a is the chief pigment involved in photosynthesis.
Light Reaction
Occurs in the thylakoid membrane.
Major Events
Absorption of light energy
Splitting of water (Photolysis)
Oxygen release
ATP formation
NADPH formation
Photolysis of Water
2H₂O → 4H⁺ + 4e⁻ + O₂
Products
ATP
NADPH
Oxygen
Photosystems
Photosystem II (PS II)
Reaction center P680
First photosystem to function
Photosystem I (PS I)
Reaction center P700
Produces NADPH
NEET Favorite Question
Which photosystem participates first in light reaction?
Answer: Photosystem II
Electron Transport System
Electrons move through:
PS II → PQ → Cyt b6f → PC → PS I → Fd → NADP
This movement generates ATP.
Cyclic and Non-Cyclic Photophosphorylation
Feature
Cyclic
Non-Cyclic
Photosystem
PS I
PS I & PS II
ATP
Produced
Produced
NADPH
Not produced
Produced
Oxygen
Not released
Released
Dark Reaction (Calvin Cycle)
Occurs in the stroma.
Three Phases
Carboxylation
Reduction
Regeneration
Key Enzyme
RuBisCO
RuBisCO is the most abundant enzyme on Earth.
First Stable Product
3-Phosphoglyceric Acid (3-PGA)
C3 Plants
Examples:
Wheat
Rice
Sunflower
Characteristics
First product: 3-PGA
Calvin cycle only
Less efficient under high temperature
C4 Plants
Examples:
Maize
Sugarcane
Sorghum
Characteristics
First product: Oxaloacetic Acid (OAA)
Kranz anatomy present
Higher photosynthetic efficiency
NCERT Important Line
Kranz anatomy is a characteristic feature of C4 plants.
Photorespiration
Occurs when RuBisCO acts as oxygenase.
Consequences
Loss of fixed carbon
Energy wastage
Reduced productivity
Absent In
C4 plants
C3 vs C4 Plants
Feature
C3
C4
First Product
3-PGA
OAA
Kranz Anatomy
Absent
Present
Photorespiration
High
Negligible
Efficiency
Lower
Higher
Most Important NCERT Points
Remember These
Chlorophyll a is the chief pigment.
PS II functions before PS I.
RuBisCO is the most abundant enzyme.
ATP and NADPH are produced during light reaction.
Calvin cycle occurs in the stroma.
Kranz anatomy is present in C4 plants.
Photorespiration reduces plant productivity.
NEET PYQ-Based Questions
Q1. Which pigment acts as the reaction center in Photosystem I?
A. Chlorophyll b
B. P700
C. P680
D. Carotene
Answer: B. P700
Q2. First stable product of Calvin cycle is:
A. OAA
B. RuBP
C. PGA
D. PEP
Answer: C. PGA
Q3. Kranz anatomy is found in:
A. Wheat
B. Rice
C. Maize
D. Sunflower
Answer: C. Maize
Q4. Most abundant enzyme on Earth is:
A. DNA Polymerase
B. ATP Synthase
C. RuBisCO
D. Pepsin
Answer: C. RuBisCO
Final Revision Tips for NEET
Read every NCERT line carefully.
Memorize diagrams of chloroplast and Calvin cycle.
Practice previous year questions.
Focus on C3 vs C4 differences.
Revise photosystems and photophosphorylation repeatedly.
Conclusion
Photosynthesis in Higher Plants is one of the highest-scoring chapters in NEET Biology. Most questions are directly based on NCERT concepts, diagrams, and terminology. A strong understanding of light reaction, Calvin cycle, C3 plants, C4 plants, and photorespiration can help you secure easy marks in the exam.
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