Respiration in Plants
Process of breaking down food (C-C bonds) within the cell to release energy (ATP). It is an Amphibolic process.
1. Glycolysis (EMP Pathway)
Location: Cytoplasm. Common to both Aerobic and Anaerobic respiration.
Scheme by: Embden, Meyerhof, Parnas.
Key Steps:
- Partial Oxidation: Glucose (6C) → 2 molecules of Pyruvic Acid (3C).
- ATP Consumed:
1. Glucose → Glucose-6-P
2. Fructose-6-P → Fructose-1,6-bisP - ATP Produced (Substrate Level Phosphorylation):
1. BPGA → PGA (2 molecules)
2. PEP → Pyruvic Acid (2 molecules) - NADH Produced: GAP → BPGA (2 molecules yield 2 NADH + H+).
Net Gain: 2 ATP + 2 NADH (Directly 2 ATP).
2. Fermentation
Incomplete oxidation of glucose under anaerobic conditions (Yeast, Muscles).
- Alcoholic Fermentation (Yeast):
Pyruvic Acid → Ethanol + CO2.
Enzymes: Pyruvate decarboxylase, Alcohol dehydrogenase. - Lactic Acid Fermentation (Muscles/Bacteria):
Pyruvic Acid → Lactic Acid.
Enzyme: Lactate dehydrogenase. - Energy Yield: Less than 7% of energy in glucose is released. Net gain = 2 ATP.
3. Aerobic Respiration
Complete oxidation of glucose into CO2 and Water. Occurs in Mitochondria.
A. Link Reaction (Oxidative Decarboxylation)
Pyruvate + CoA + NAD+ → Acetyl CoA + CO2 + NADH + H+
Location: Mitochondrial Matrix. Enzyme: Pyruvate dehydrogenase.
B. Krebs Cycle (TCA Cycle)
- First Product: Citric Acid (6C). Formed by Acetyl CoA (2C) + OAA (4C).
- Decarboxylation:
1. Oxalosuccinic acid → Alpha-ketoglutaric acid (5C) + CO2
2. Alpha-ketoglutaric acid → Succinyl CoA (4C) + CO2 - ATP/GTP (SLP): Succinyl CoA → Succinic Acid.
- FADH2 production: Succinic acid → Fumaric acid.
4. ETS & Oxidative Phosphorylation
Location: Inner Mitochondrial Membrane.
| Complex | Name |
|---|
| Complex I | NADH Dehydrogenase |
| Complex II | Succinate Dehydrogenase (FADH2) |
| Complex III | Cytochrome bc1 complex |
| Complex IV | Cytochrome c Oxidase (Cyt a, a3, 2 Cu centers) |
| Complex V | ATP Synthase (F0-F1) |
- Final Electron Acceptor: Oxygen (forms metabolic water).
- Chemiosmotic Hypothesis: Proton gradient generated across inner membrane. H+ moves from Inter-membrane space to Matrix through F0.
- ATP Yield: 1 NADH = 3 ATP; 1 FADH2 = 2 ATP.
5. Respiratory Balance Sheet
Theoretical calculation for 1 Glucose molecule.
- Glycolysis: 2 ATP + 2 NADH (6 ATP) = 8 ATP.
- Link Reaction: 2 NADH (6 ATP).
- Krebs Cycle: 2 GTP (2 ATP) + 6 NADH (18 ATP) + 2 FADH2 (4 ATP) = 24 ATP.
- Total = 38 ATP.
- (In some cells, shuttle systems cost 2 ATP, net = 36 ATP).
6. Amphibolic Pathway & RQ
Amphibolic: Involved in both Anabolism (synthesis) and Catabolism (breakdown).
e.g., Acetyl CoA is used to synthesize Fatty Acids/Gibberellins. Alpha-ketoglutaric acid used for amino acid synthesis.
Respiratory Quotient (RQ)
RQ = Vol CO2 evolved / Vol O2 consumed.
- Carbohydrates: RQ = 1.0
- Fats: RQ = 0.7 (Tripalmitin)
- Proteins: RQ = 0.9
- Organic Acids: RQ > 1 (Oxalic acid = 4, Malic acid = 1.33)
HOT Questions - Respiration in Plants
Directions for Assertion & Reason:
(A) Both Assertion & Reason are true and Reason is correct explanation of Assertion.
(B) Both Assertion & Reason are true but Reason is NOT correct explanation of Assertion.
(C) Assertion is true but Reason is false.
(D) Both Assertion & Reason are false.
Q1
Assertion: 36 ATP molecules are produced during aerobic respiration of one molecule of
glucose.
Reason: 2 ATP molecules are consumed in transporting 2 NADH molecules from cytoplasm to
mitochondria.
Correct Answer:
(A)
The Gross total is 38 ATP. But the Glycerol Phosphate Shuttle consumes 2 ATP to move cytosolic NADH to
mitochondria, resulting in net 36 ATP (common in eukaryotes).
Q2
Assertion: The RQ of fats is less than 1.
Reason: Fats contain less oxygen as compared to carbohydrates.
Correct Answer:
(A)
Since fats are poor in oxygen, they require more external oxygen for oxidation, hence volume of O2
consumed > CO2 evolved. RQ < 1.
Q3
How many ATP are yielded by the complete oxidation of one molecule of Pyruvic acid in Mitochondria?
Correct Answer:
(B)
Pyruvic acid (Link Reaction -> 1 NADH = 3 ATP). Krebs (3 NADH=9, 1 FADH2=2, 1 GTP=1 -> 12). Total =
3 + 12 = 15 ATP.
Q4
Which of the following is the connecting link between Glycolysis and Krebs cycle?
A.
Pyruvic acid
B.
Acetyl CoA
C.
Citric Acid
D.
Phosphoglyceric acid
Correct Answer:
(B)
Acetyl CoA is formed from Pyruvate (product of glycolysis) and enters Krebs cycle.
Q5
The final electron acceptor in the electron transport system is:
A.
Cytochrome b
B.
Cytochrome a3
C.
Oxygen
D.
Hydrogen
Correct Answer:
(C)
Oxygen acts as the final hydrogen acceptor to form water.
Q6
Which of the following is a 5-Carbon compound?
A.
Oxaloacetic acid
B.
Citric acid
C.
Alpha-ketoglutaric acid
D.
Succinic acid
Correct Answer:
(C)
Alpha-ketoglutarate is 5C. Oxaloacetate/Succinic are 4C. Citric is 6C.
Q7
In Glycolysis, ATP is synthesized by substrate level phosphorylation during the conversion of:
A.
1,3-bisPGA to 3-PGA
B.
Glucose to Glucose-6-P
C.
Fructose-6-P to Fructose-1,6-bisP
D.
3-PGA to 2-PGA
Correct Answer:
(A)
BPGA to PGA is an energy yielding step (ATP formation).
Q8
Which complex in ETS contains two copper centers?
A.
Complex I
B.
Complex III
C.
Complex IV
D.
Complex V
Correct Answer:
(C)
Complex IV (Cytochrome c Oxidase) contains Cyt a, a3 and two Copper centers.
Q9
Respiratory Quotient (RQ) for oxalic acid is:
A. 1
B.
0.7
C.
Infinite
D. 4
Correct Answer:
(D)
Organic acids have RQ > 1. Oxalic acid RQ is 4.
Q10
F0-F1 particles are located on:
A.
Inner mitochondrial membrane
B.
Outer mitochondrial membrane
C.
Matrix
D.
Thylakoid membrane
Correct Answer:
(A)
They are ATP synthase complexes located on the inner membrane (Cristae).
Quick Revision
Facts
1. Cellular Respiration
Mechanism of breakdown of food materials within cell to
release energy and trap it as ATP.
[NCERT]
2. Amphibolic Pathway
Respiration involves both breaking down (Catabolism) and
synthesis (Anabolism) of substrates.
[NCERT]
3. Glycolysis
Occurs in cytoplasm. Glucose (6C) broken into 2 Pyruvic acid
(3C). No Oxygen required.
[NCERT]
4. EMP Pathway
Glycolysis scheme given by Embden, Meyerhof, and Parnas.
[NCERT]
5. Net Gain (Glycolysis)
2 ATP directly produced + 2 NADH molecules.
[NCERT]
6. Fermentation
Incomplete oxidation of glucose under anaerobic conditions.
Net gain 2 ATP.
[NCERT]
7. Alcoholic Fermentation
Yeast. Pyruvic acid -> Ethanol + CO2. Enzymes: Pyruvate
decarboxylase, Alcohol dehydrogenase.
[NCERT]
8. Yeast Poisoning
Yeasts poison themselves to death when alcohol concentration
reaches about 13%.
[NCERT]
9. Lactic Acid Fermentation
In muscles/bacteria. Pyruvic acid -> Lactic acid. No CO2
evolved.
[NCERT]
10. Aerobic Respiration
Complete oxidation of organic substances in presence of
oxygen. Releases CO2, Water and Energy.
[NCERT]
11. Link Reaction
Pyruvate to Acetyl CoA. Oxidative decarboxylation. Occurs in
Mitochondrial Matrix.
[NCERT]
12. Krebs Cycle
Also known as Tricarboxylic Acid (TCA) Cycle or Citric Acid
Cycle. Hans Krebs.
[NCERT]
13. Citric Acid Synthesis
First step of Krebs cycle. Acetyl CoA + Oxaloacetic Acid +
Water -> Citric Acid.
[NCERT]
14. Decarboxylation in TCA
Occurs at two steps. Oxalosuccinic -> Alpha-ketoglutarate.
Alpha-ketoglutarate -> Succinyl CoA.
[NCERT]
15. Substrate Level Phosphorylation (TCA)
Formation of GTP during conversion of Succinyl CoA to
Succinic Acid.
[NCERT]
16. ETS Location
Electron Transport System is located in the Inner
Mitochondrial Membrane.
[NCERT]
17. Complex I
NADH Dehydrogenase complex. Oxidises NADH produced in
matrix.
[NCERT]
18. Complex II
Succinate Dehydrogenase. Receives electrons from FADH2.
[NCERT]
19. Ubiquinone (UQ)
Mobile carrier located within the inner membrane. Receives
electrons from Complex I and II.
[NCERT]
20. Complex IV
Cytochrome c oxidase. Contains Cytochromes a and a3, and two
copper centers.
[NCERT]
21. Final Acceptor
Oxygen is the final acceptor of electrons and protons,
forming metabolic water.
[NCERT]
22. Complex V (ATP Synthase)
Consists of F0 (Integral membrane protein, proton channel)
and F1 (Peripheral headpiece, ATP synthesis).
[NCERT]
23. Proton Gradient
Passage of 2H+ through F0 releases enough energy for
synthesis of 1 ATP.
[NCERT]
24. NADH Oxidation
Oxidation of one molecule of NADH gives 3 molecules of ATP.
[NCERT]
25. FADH2 Oxidation
Oxidation of one molecule of FADH2 produces 2 molecules of
ATP.
[NCERT]
26. Net ATP (Aerobic)
There can be a net gain of 38 ATP molecules during aerobic
respiration of one glucose (Theoretical).
[NCERT]
27. RQ of Carbohydrates
Respiratory Quotient (RQ) is 1.0 (Volume of CO2 = Volume of
O2).
[NCERT]
28. RQ of Fats
RQ is less than 1. (Tripalmitin RQ = 0.7). Fats need more O2
for oxidation.
[NCERT]
30. RQ of Organic Acids
RQ is greater than 1. (e.g., Organic acids are rich in O2).
[NEET]
31. Acetyl CoA Function
Connecting link between Glycolysis and Krebs cycle. Also
precursor for fatty acid synthesis.
[NCERT]
32. Alpha-Ketoglutaric Acid
Raw material for amino acid synthesis (via Reductive
Amination).
[NCERT]
33. Succinyl CoA
Precursor for synthesis of Chlorophyll and Cytochromes.
[NEET]
34. Floating Respiration
Respiration using Carbohydrates or Fats (floating
inclusions) as substrate.
[NEET]
35. Protoplasmic Respiration
Respiration using Proteins as substrate. Occurs during
starvation / disease.
[NEET]
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