Introduction
Respiration is a vital metabolic process in plants through which stored food (glucose) is oxidized to release energy. This energy is used for growth, repair, transport, and other life processes.
Unlike animals, plants do not have specialized respiratory organs. Gas exchange occurs through stomata, lenticels, and root surfaces.
What is Respiration?
Respiration is the biochemical process of breaking down organic substances (like glucose) to release energy in the form of ATP.
General Equation of Respiration
C6H12O6+6O2→6CO2+6H2O+Energy (ATP)
Types of Respiration
1. Aerobic Respiration
- Occurs in the presence of oxygen
- Complete oxidation of glucose
- Produces large amount of energy (~36–38 ATP)
Equation:
Glucose + Oxygen → CO₂ + H₂O + Energy
2. Anaerobic Respiration
- Occurs in absence of oxygen
- Incomplete breakdown of glucose
- Produces less energy (~2 ATP)
Examples:
- In yeast: Ethanol + CO₂
- In muscles (rare in plants): Lactic acid
Amphibolic Pathway
Respiration is called an amphibolic pathway because it involves both:
- Catabolism: Breakdown of glucose
- Anabolism: Synthesis of biomolecules
Respiratory Quotient (RQ)
RQ = CO₂ released / O₂ consumed
Values of RQ
- Carbohydrates: 1
- Fats: < 1
- Organic acids: > 1
Steps of Respiration
Respiration in plants occurs in multiple steps:
1. Glycolysis (EMP Pathway)
- Occurs in cytoplasm
- Does not require oxygen
- Glucose (6C) → 2 Pyruvate (3C)
Key Features
- Produces 2 ATP (net gain)
- Produces 2 NADH
- Common to both aerobic and anaerobic respiration
2. Oxidative Decarboxylation (Link Reaction)
- Occurs in mitochondria
- Pyruvate → Acetyl CoA
Products:
- CO₂ released
- NADH formed
3. Krebs Cycle (Citric Acid Cycle)
- Occurs in mitochondrial matrix
- Acetyl CoA enters cycle
Key Outputs (per glucose):
- 2 ATP
- 6 NADH
- 2 FADH₂
- 4 CO₂
4. Electron Transport System (ETS)
- Occurs in inner mitochondrial membrane
- Electrons transferred through carriers
Final Step:
- Oxygen acts as final electron acceptor
- Water is formed
ATP Production:
- Maximum ATP generated here
Total ATP Yield
| Stage | ATP Produced |
|---|---|
| Glycolysis | 2 |
| Krebs Cycle | 2 |
| ETS | ~32–34 |
| Total | 36–38 ATP |
Fermentation
Fermentation is a type of anaerobic respiration.
Types:
1. Alcoholic Fermentation
- Pyruvate → Ethanol + CO₂
- Occurs in yeast
2. Lactic Acid Fermentation
- Pyruvate → Lactic acid
- Rare in plants
Energy Relations
- ATP is the energy currency of the cell
- Stored energy released in a stepwise manner
- Prevents loss of energy as heat
Factors Affecting Respiration
1. Temperature
- Higher temperature → faster respiration
- Extreme heat → enzyme denaturation
2. Oxygen Availability
- Required for aerobic respiration
- Low oxygen → anaerobic respiration
3. Water
- Necessary for enzyme activity
4. Substrate Availability
- More glucose → increased respiration
Differences Between Aerobic and Anaerobic Respiration
| Feature | Aerobic | Anaerobic |
|---|---|---|
| Oxygen | Required | Not required |
| Breakdown | Complete | Incomplete |
| ATP yield | High | Low |
| End products | CO₂ + H₂O | Ethanol/Lactic acid |
Differences Between Respiration and Photosynthesis
| Feature | Respiration | Photosynthesis |
|---|---|---|
| Type | Catabolic | Anabolic |
| Energy | Released | Stored |
| Occurs in | All cells | Chloroplast |
| Oxygen | Consumed | Released |
Significance of Respiration in Plants
- Provides energy (ATP)
- Supports growth and development
- Helps in biosynthesis
- Maintains metabolic activities
Important NEET & CBSE Points
- Glycolysis occurs in cytoplasm
- Krebs cycle occurs in mitochondria
- Final electron acceptor = Oxygen
- ATP = Energy currency
- RQ of carbohydrate = 1
- Amphibolic pathway = Respiration
Quick Revision Notes
- Respiration = energy release
- Glycolysis → Krebs → ETS
- Aerobic = high energy
- Anaerobic = low energy
- ATP is produced mainly in ETS
Frequently Asked Questions (FAQs)
Q1. What is respiration in plants?
It is the process of breaking down glucose to release energy.
Q2. Where does glycolysis occur?
In the cytoplasm.
Q3. What is the final electron acceptor?
Oxygen.
Q4. Why is respiration called amphibolic?
Because it involves both breakdown and synthesis pathways.
Conclusion
Respiration in plants is a complex yet essential process that ensures continuous energy supply for all life activities. Understanding its pathways, mechanisms, and significance is crucial for excelling in CBSE board exams and NEET.