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Q4:
What are the major transport mechanisms for $CO_2$? Explain.
Solution :
Given Variables & Theoretical Foundation
Carbon dioxide ($CO_2$) is a byproduct of cellular metabolism. Since its partial pressure in systemic tissues ($PCO_2 \approx 45 \, mmHg$) is higher than in oxygenated blood ($PCO_2 \approx 40 \, mmHg$), it diffuses into the blood. Transport occurs via three primary mechanisms determined by solubility and chemical equilibrium constants [Per Fick’s Law of Diffusion and the Bohr Effect].
Step 1: Transport as Dissolved Gas in Plasma
A minor fraction of $CO_2$ is physically dissolved in the blood plasma. Due to its higher solubility compared to $O_2$, approximately 7% of total $CO_2$ is transported in this state.
- Mechanism: Simple diffusion driven by the partial pressure gradient.
- Efficiency: Limited by the solubility coefficient of $CO_2$ in aqueous plasma [Per Henry’s Law].
Step 2: Transport as Carbaminohemoglobin
Approximately 20–25% of $CO_2$ binds directly to the amino groups of the globin chain of hemoglobin, forming carbaminohemoglobin ($HbNHCO_2$).
- Reaction: $Hb + CO_2 \rightleftharpoons HbNHCO_2$.
- Regulation: Binding is facilitated by low $PO_2$ in tissues. As hemoglobin releases $O_2$, its affinity for $CO_2$ increases [The Haldane Effect].
Step 3: Transport as Bicarbonate Ions ($HCO_3^-$)
The majority, approximately 70%, of $CO_2$ is transported as bicarbonate. This mechanism is highly efficient due to the enzymatic activity of Carbonic Anhydrase.
- Intracellular Reaction: $CO_2$ enters erythrocytes and combines with $H_2O$ to form $H_2CO_3$ (Carbonic acid), catalyzed by the enzyme Carbonic Anhydrase.
- Dissociation: $H_2CO_3 \xrightarrow{Carbonic\,Anhydrase} H^+ + HCO_3^-$.
- Ionic Equilibrium (Chloride Shift): To maintain electrochemical neutrality, $HCO_3^-$ ions diffuse out of the RBC into the plasma, and $Cl^-$ ions diffuse into the RBC [Known as the Hamburger Phenomenon or Chloride Shift].
Summary Comparison Table
| Mechanism | Percentage Transported | Primary Medium |
|---|---|---|
| Dissolved in Plasma | ~7% | Plasma |
| Carbaminohemoglobin | ~23% | Erythrocytes (Hemoglobin) |
| Bicarbonate Ions | ~70% | Plasma (via RBC conversion) |
Visual Representation of $CO_2$ Transport Dynamics
Final Solution: $CO_2$ is transported via three mechanisms: 7% dissolved in plasma, 20-25% bound to hemoglobin as carbaminohemoglobin, and 70% converted to bicarbonate ions ($HCO_3^-$) in the erythrocytes and transported in the plasma.
More Questions from Class 11 Biology Breathing and Exchange of Gases EXERCISES
- Q1: Define vital capacity. What is its significance?
- Q2: State the volume of air remaining in the lungs after a normal breathing.
- Q3: Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system. Why?
- Q5: What will be the $pO_2$ and $pCO_2$ in the atmospheric air compared to those in the alveolar air ?
- Q6: Explain the process of inspiration under normal conditions.
- Q7: How is respiration regulated?
- Q8: What is the effect of $pCO_2$ on oxygen transport?
- Q9: What happens to the respiratory process in a man going up a hill?
- Q10: What is the site of gaseous exchange in an insect?
- Q11: Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?
- Q12: Have you heard about hypoxia? Try to gather information about it, and discuss with your friends.
- Q13(a): Distinguish between (a) IRV and ERV
- Q13(b): Distinguish between (b) Inspiratory capacity and Expiratory capacity.
- Q13(c): Distinguish between (c) Vital capacity and Total lung capacity.
- Q14: What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.
CBSE Solutions for Class 11 Biology Breathing and Exchange of Gases
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
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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