📚 Quick Summary
Respiration in Plants Class 11 Biology is an important NCERT topic for NEET 2027 Biology. It explains how organisms obtain usable energy from food through processes such as glycolysis, fermentation, the Krebs cycle and the electron transport system.
For NEET preparation, pay special attention to the site of each process, major products, ATP production and the sequence of respiratory pathways.
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Explore NEET Biology Resources →Respiration in Plants Class 11 Biology: NCERT Notes for NEET 2027
Respiration in Plants Class 11 Biology is a fundamental topic in plant physiology and an important part of NCERT Biology for students preparing for NEET 2027.
Respiration is the biochemical process through which cells obtain usable energy from organic molecules. In plants, glucose can be broken down through glycolysis, fermentation or aerobic respiration depending on cellular conditions.
These notes cover the major concepts of the NCERT chapter Respiration in Plants in a simple, revision-friendly format.
Respiration in Plants: Chapter at a Glance
| Process | Main Site | Major Outcome |
|---|---|---|
| Glycolysis | Cytoplasm | Pyruvate |
| Fermentation | Cytoplasm | Lactic acid or ethanol + CO₂ |
| Krebs Cycle | Mitochondrial matrix | CO₂, NADH, FADH₂ and ATP/GTP |
| ETS | Inner mitochondrial membrane | ATP formation and water |
1. What Is Respiration?
Respiration is a biochemical process in which organic substances are broken down through a series of reactions to release energy that can be captured in the form of ATP.
In aerobic respiration, glucose is ultimately oxidised to carbon dioxide and water, with energy conserved in ATP.
2. Types of Respiration
A. Aerobic Respiration
- Occurs when oxygen is available for aerobic metabolism.
- Glucose is extensively oxidised.
- Produces much more ATP than fermentation.
- Major stages occur in the cytoplasm and mitochondria.
B. Anaerobic Respiration / Fermentation
In the NCERT context, fermentation refers to the anaerobic breakdown of pyruvate into products such as ethanol and carbon dioxide or lactic acid, depending on the organism or tissue.
- Does not require oxygen as the terminal electron acceptor.
- Occurs in the cytoplasm.
- Produces much less ATP than aerobic respiration.
3. Glycolysis – The First Stage
Glycolysis is the pathway in which one molecule of glucose is converted into two molecules of pyruvate.
It occurs in the cytoplasm and is also known as the EMP pathway, named after Embden, Meyerhof and Parnas.
Important Features of Glycolysis
- Starting molecule: Glucose
- End product: 2 Pyruvate
- Site: Cytoplasm
- Net ATP gain: 2 ATP
- NADH produced: 2 NADH
Glycolysis = Glucose → 2 Pyruvate
Site = Cytoplasm
4. Fate of Pyruvate
The fate of pyruvate depends on the availability of oxygen and the metabolic conditions of the cell.
Pyruvate can undergo different pathways:
- Lactic acid fermentation
- Alcoholic fermentation
- Aerobic respiration
4.1 Lactic Acid Fermentation
Under anaerobic conditions, pyruvate can be converted into lactic acid in certain cells and microorganisms.
Pyruvate → Lactic acid
4.2 Alcoholic Fermentation
In yeast, pyruvate is converted into ethanol and carbon dioxide.
Pyruvate → Ethanol + CO₂
Yeast fermentation → Ethanol + CO₂
Lactic fermentation → Lactic acid
5. Aerobic Respiration
When oxygen is available, pyruvate is transported into the mitochondrion and enters the aerobic respiratory pathway.
The major stages include:
- Oxidative decarboxylation of pyruvate
- Krebs cycle
- Electron transport system
- Oxidative phosphorylation
6. Oxidative Decarboxylation of Pyruvate
Before entering the Krebs cycle, pyruvate is converted into acetyl-CoA.
This reaction takes place in the mitochondrial matrix in eukaryotic cells.
The process releases carbon dioxide and produces NADH.
Pyruvate → Acetyl-CoA + CO₂ + NADH
7. Krebs Cycle / Citric Acid Cycle
The Krebs cycle, also called the citric acid cycle or TCA cycle, is a major stage of aerobic respiration.
In eukaryotic cells, it occurs in the mitochondrial matrix.
Important Points
- Acetyl-CoA enters the cycle.
- Carbon dioxide is released.
- NADH and FADH₂ are generated.
- A small amount of ATP/GTP is formed.
- Reduced electron carriers transfer high-energy electrons to the ETS.
Products of Krebs Cycle per Glucose
Since one glucose molecule produces two acetyl-CoA molecules, the Krebs cycle turns twice per glucose molecule.
- 4 CO₂
- 6 NADH
- 2 FADH₂
- 2 ATP/GTP
8. Electron Transport System (ETS)
The electron transport system is located on the inner mitochondrial membrane in eukaryotic cells.
Electrons carried by NADH and FADH₂ pass through electron carriers. The energy released is used to establish a proton gradient that drives ATP synthesis.
Oxygen acts as the final electron acceptor in aerobic respiration, ultimately leading to the formation of water.
ETS → Inner mitochondrial membrane
Final electron acceptor → Oxygen
9. Oxidative Phosphorylation
The synthesis of ATP using the energy released during electron transport is called oxidative phosphorylation.
ATP synthase uses the proton gradient across the inner mitochondrial membrane to synthesise ATP.
10. Respiratory Balance Sheet
The complete oxidation of one glucose molecule involves glycolysis, pyruvate oxidation, the Krebs cycle and the electron transport system.
The exact ATP accounting depends on the assumptions used for transfer of reducing equivalents and the cellular system. Therefore, for NEET preparation, focus on the NCERT treatment and the underlying pathway rather than memorising an isolated ATP number without context.
11. Respiration as an Amphibolic Pathway
Respiratory pathways are called amphibolic because they play roles in both catabolism and anabolism.
Respiratory intermediates can be diverted for the synthesis of different cellular compounds, while some compounds can enter respiratory pathways for energy production.
12. Respiratory Quotient (RQ)
The respiratory quotient is the ratio of the volume of carbon dioxide evolved to the volume of oxygen consumed during respiration.
RQ = CO₂ evolved ÷ O₂ consumed
Important Examples
- For carbohydrates, RQ is generally 1.
- For fats, RQ is generally less than 1.
- For organic acids, RQ can be greater than 1 in certain cases.
13. Aerobic Respiration vs Fermentation
| Feature | Aerobic Respiration | Fermentation |
|---|---|---|
| Oxygen | Required for aerobic pathway | Not required |
| Major site | Cytoplasm + mitochondria | Cytoplasm |
| Glucose breakdown | Extensive | Incomplete |
| Products | CO₂ and H₂O | Lactic acid or ethanol + CO₂ |
| ATP production | Much higher | Low |
14. Important Sites to Remember for NEET
| Process | Site |
|---|---|
| Glycolysis | Cytoplasm |
| Fermentation | Cytoplasm |
| Pyruvate oxidation | Mitochondrial matrix |
| Krebs cycle | Mitochondrial matrix |
| ETS | Inner mitochondrial membrane |
15. Important NEET MCQs on Respiration in Plants
1. Glycolysis occurs in:
A. Nucleus
B. Cytoplasm
C. Mitochondrial matrix
D. Chloroplast
Answer: B. Cytoplasm
2. The end product of glycolysis is:
A. Acetyl-CoA
B. Ethanol
C. Pyruvate
D. Carbon dioxide
Answer: C. Pyruvate
3. Glycolysis is also called:
A. TCA pathway
B. EMP pathway
C. Calvin cycle
D. C4 pathway
Answer: B. EMP pathway
4. The Krebs cycle occurs mainly in the:
A. Cytoplasm
B. Nucleus
C. Mitochondrial matrix
D. Ribosome
Answer: C. Mitochondrial matrix
5. In aerobic respiration, the final electron acceptor is:
A. Carbon dioxide
B. Glucose
C. Oxygen
D. NADH
Answer: C. Oxygen
6. Alcoholic fermentation in yeast produces:
A. Lactic acid only
B. Ethanol and CO₂
C. Acetyl-CoA and oxygen
D. Glucose and oxygen
Answer: B. Ethanol and CO₂
7. The electron transport system is located in the:
A. Outer mitochondrial membrane
B. Inner mitochondrial membrane
C. Cytoplasm
D. Nucleus
Answer: B. Inner mitochondrial membrane
16. Respiration in Plants: NEET Quick Revision
- Glycolysis: Glucose → 2 Pyruvate.
- Site of glycolysis: Cytoplasm.
- EMP: Embden-Meyerhof-Parnas pathway.
- Fermentation: Anaerobic breakdown of pyruvate.
- Yeast: Ethanol + CO₂.
- Krebs cycle: Mitochondrial matrix.
- ETS: Inner mitochondrial membrane.
- Final electron acceptor: Oxygen.
- RQ: CO₂ evolved ÷ O₂ consumed.
- Respiratory pathway: Amphibolic in nature.
17. How to Study Respiration in Plants for NEET 2027
- Read the NCERT chapter carefully before using additional reference material.
- Memorise the location of glycolysis, Krebs cycle and ETS.
- Understand the fate of pyruvate under different conditions.
- Practise questions involving ATP, NADH, FADH₂ and respiratory quotient.
- Revise the respiratory pathway as a flowchart.
- Solve NEET previous-year questions after completing the NCERT revision.
🧬 Respiration Flowchart
Glucose
↓
Glycolysis
↓
2 Pyruvate
↓
Acetyl-CoA
↓
Krebs Cycle
↓
NADH + FADH₂
↓
ETS
↓
ATP + H₂O
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Explore NEET Biology Resources →Final Revision
Respiration in Plants Class 11 Biology becomes easier when the pathway is understood as a sequence:
Glucose → Glycolysis → Pyruvate → Acetyl-CoA → Krebs Cycle → ETS
For NEET 2027, focus on the site, products and major events of each stage, along with fermentation, respiratory quotient and the amphibolic nature of respiration.
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