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Q9:
Discuss “The respiratory pathway is an amphibolic pathway.”
Solution :
Definition of Amphibolic Pathway
The term amphibolic is derived from the Greek word 'amphibolos', meaning 'thrown on both sides'. In metabolic biochemistry, a pathway is termed amphibolic when it functions in both catabolism (degradation of molecules to release energy) and anabolism (synthesis of complex molecules from simpler precursors).
Step 1: The Catabolic Role (Energy Yield)
Cellular respiration serves primarily as a catabolic process. Carbohydrates, fats, and proteins are broken down into smaller components to generate ATP, $NADH$, and $FADH_2$.
- Carbohydrates: Glycolysis converts glucose into pyruvate, which enters the Krebs cycle via Acetyl-CoA.
- Fats: Fatty acids undergo $\beta$-oxidation to form Acetyl-CoA.
- Proteins: Deaminated amino acids enter the respiratory pathway at various stages (e.g., as Pyruvate, Acetyl-CoA, or $\alpha$-ketoglutarate).
Step 2: The Anabolic Role (Biosynthetic Precursors)
The respiratory pathway serves as a reservoir of metabolites that are withdrawn for the synthesis of cellular structures. The metabolic intermediates generated in the Citric Acid (Krebs) cycle are redirected toward biosynthetic processes [Per the principle of Metabolic Flux].
Step 3: Analytical Evidence of Interconnection
The following table illustrates the diversion of respiratory intermediates into biosynthetic pathways:
| Respiratory Intermediate | Anabolic Product |
|---|---|
| Acetyl-CoA | Fatty acids, Steroids, Terpenes |
| $\alpha$-Ketoglutarate | Glutamate and other amino acids |
| Oxaloacetate | Aspartate and other amino acids |
Step 4: Theoretical Justification
The pathway is considered amphibolic because the flux of molecules is bidirectional. When the cell requires energy, intermediates like Acetyl-CoA are oxidized via the Citric Acid Cycle [Catabolic]. Conversely, when the cell requires structural components for growth and repair, these same intermediates are siphoned off to synthesize essential organic macromolecules [Anabolic].
Final Solution: The respiratory pathway is defined as amphibolic because it integrates both catabolic breakdown (generating energy from respiratory substrates) and anabolic synthesis (utilizing respiratory intermediates as building blocks for cellular components), thereby maintaining the metabolic balance of the living cell.
More Questions from Class 11 Biology Respiration in Plants EXERCISES
- Q1(a): Differentiate between (a) Respiration and Combustion
- Q1(b): Differentiate between (b) Glycolysis and Krebs’ cycle
- Q1(c): Differentiate between (c) Aerobic respiration and Fermentation
- Q2: What are respiratory substrates? Name the most common respiratory substrate.
- Q3: Give the schematic representation of glycolysis?
- Q4: What are the main steps in aerobic respiration? Where does it take place?
- Q5: Give the schematic representation of an overall view of Krebs’ cycle.
- Q6: Explain ETS.
- Q7(a): Distinguish between the following: (a) Aerobic respiration and Anaerobic respiration
- Q7(b): Distinguish between the following: (b) Glycolysis and Fermentation
- Q7(c): Distinguish between the following: (c) Glycolysis and Citric acid Cycle
- Q8: What are the assumptions made during the calculation of net gain of ATP?
- Q10: Define RQ. What is its value for fats?
- Q11: What is oxidative phosphorylation?
- Q12: What is the significance of step-wise release of energy in respiration?
CBSE Solutions for Class 11 Biology Respiration in Plants
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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