Photosynthesis vs Respiration: Complete NEET Guide

These two fundamental processes are among the most important topics in NEET Biology, appearing in 4-6 questions every year. Understanding their differences and similarities is crucial for scoring maximum marks.

Quick Comparison Table

Detailed Process Analysis

Photosynthesis: The Food Factory

Overall Equation: 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂

Two Main Phases:

1. Light Reactions (Photo-chemical phase)

   • Location: Thylakoid membranes
   • Products: ATP, NADPH, O₂
   • Key processes: Photolysis, electron transport

2. Dark Reactions (Bio-chemical phase)

   • Location: Stroma
   • Process: Calvin Cycle (C₃ cycle)
   • Product: Glucose formation

Respiration: The Powerhouse

Overall Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP

Three Main Phases:

1. Glycolysis

   • Location: Cytoplasm
   • Products: 2 Pyruvate + 2 ATP + 2 NADH

2. Krebs Cycle (Citric Acid Cycle)

   • Location: Mitochondrial matrix
   • Products: 2 ATP + 6 NADH + 2 FADH₂

3. Electron Transport Chain (ETC)

   • Location: Inner mitochondrial membrane
   • Products: 34 ATP (via oxidative phosphorylation)

Key Differences for NEET

1. Metabolic Nature

• Photosynthesis: Anabolic process (builds molecules)
• Respiration: Catabolic process (breaks molecules)

2. Energy Flow

• Photosynthesis: Endergonic (requires energy input)
• Respiration: Exergonic (releases energy)

3. Gas Exchange

• Photosynthesis: Takes in CO₂, releases O₂
• Respiration: Takes in O₂, releases CO₂

4. Pigment Involvement

• Photosynthesis: Requires chlorophyll and accessory pigments
• Respiration: No pigments required

NEET Important Points

1. Compensation Point: When photosynthesis rate = respiration rate
2. R.Q. (Respiratory Quotient): CO₂ evolved / O₂ consumed
3. Photosynthetic Quotient: O₂ evolved / CO₂ absorbed

Common NEET Questions Pattern

• Direct comparison questions (most common)
• Site/location identification
• Product/reactant identification
• Equation balancing
• Diagram-based questions

Memory Tricks

For Photosynthesis Phases: "Light reactions need Light" (Thylakoid) "Dark reactions don't need Direct light" (Stroma)

For Respiration Stages: "Glycolysis in General cytoplasm" "Krebs in Kitchen (Matrix)" "ETC on inner Envelope"

Practice Questions

1. Where does the light reaction of photosynthesis take place?
2. What is the net ATP gain from one glucose molecule in aerobic respiration?
3. Which phase of respiration occurs in the absence of oxygen?

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