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Q6:
Explain ETS.
Solution :
1. Theoretical Foundation of the Electron Transport System (ETS)
The Electron Transport System (ETS) is the final stage of aerobic respiration, occurring within the inner mitochondrial membrane (cristae). Its primary function is to oxidize the reduced coenzymes ($NADH + H^+$ and $FADH_2$) generated during glycolysis, the link reaction, and the Krebs cycle to produce ATP via oxidative phosphorylation [Per the Chemiosmotic Hypothesis of Peter Mitchell].
2. Structural Organization of Complexes
The ETS consists of four major protein complexes and two mobile electron carriers:
| Complex | Name | Function |
|---|---|---|
| Complex I | NADH dehydrogenase | Oxidizes NADH to $NAD^+$; pumps $H^+$ into intermembrane space. |
| Complex II | Succinate dehydrogenase | Oxidizes $FADH_2$ to $FAD$; part of the Krebs cycle. |
| Complex III | Cytochrome $bc_1$ complex | Transfers electrons from ubiquinone to cytochrome c. |
| Complex IV | Cytochrome c oxidase | Contains cytochromes $a$ and $a_3$; reduces $O_2$ to $H_2O$. |
3. Sequential Electron Flow and Proton Gradient
Step 1: Oxidation of NADH and $FADH_2$
Electrons from $NADH$ enter at Complex I. Electrons from $FADH_2$ enter at Complex II. Both pathways converge at Ubiquinone (UQ), a lipid-soluble carrier [Per the Lipid Bilayer Fluid Mosaic Model].
Step 2: Ubiquinone to Cytochrome c
Ubiquinone transfers electrons to Complex III. From here, electrons are transferred to Cytochrome c, a small protein attached to the outer surface of the inner membrane, which acts as a mobile carrier between Complex III and IV.
Step 3: The Terminal Electron Acceptor
At Complex IV, electrons are finally passed to molecular oxygen ($O_2$), which acts as the terminal electron acceptor. By combining with protons ($H^+$) from the matrix, oxygen is reduced to form metabolic water:
$1/2 O_2 + 2H^+ + 2e^- \rightarrow H_2O$
4. Visual Representation of the Electron Transport Chain
5. Oxidative Phosphorylation
As electrons move through Complexes I, III, and IV, energy is released and used to pump protons ($H^+$) from the mitochondrial matrix into the intermembrane space. This creates an electrochemical proton gradient [Per the Chemiosmotic Coupling Theory].
The accumulation of protons creates a Proton Motive Force (PMF). Protons flow back into the matrix through the $F_0-F_1$ ATP synthase complex. The energy released by this facilitated diffusion drives the synthesis of ATP from ADP and inorganic phosphate ($Pi$):
$ADP + Pi \rightarrow ATP$
Final Solution: The Electron Transport System is the metabolic pathway in the mitochondria where NADH and $FADH_2$ are oxidized to generate a proton gradient, facilitating the production of ATP via ATP synthase, with oxygen serving as the final electron acceptor to form water.
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.
- 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?
- Q9: Discuss “The respiratory pathway is an amphibolic pathway.”
- 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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