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Q9:
What happens to the respiratory process in a man going up a hill?
Solution :
Step 1: Physiological Impact of Decreased Partial Pressure
As an individual ascends to a higher altitude, the total atmospheric pressure decreases [Per the Dalton’s Law of Partial Pressures]. Although the percentage composition of oxygen in the atmosphere remains constant at approximately $21\%$, the partial pressure of oxygen ($pO_2$) drops significantly.
The relationship is defined as: $pO_2 = P_{atm} \times F_{O_2}$, where $P_{atm}$ is the ambient barometric pressure and $F_{O_2}$ is the fractional concentration of oxygen. As $P_{atm}$ falls with increasing altitude, the diffusion gradient between the alveolar air and the pulmonary capillary blood narrows.
Step 2: Immediate Compensatory Mechanisms (Acute Mountain Sickness Phase)
To counteract the diminished oxygen supply (hypoxia), the human body activates several homeostatic responses:
- Increased Ventilation Rate: Peripheral chemoreceptors located in the carotid bodies and aortic arch detect the drop in $pO_2$. These sensors send afferent signals to the medulla oblongata to increase the rate and depth of respiration (hyperpnea) [Based on the Respiratory Control Center feedback loop].
- Tachycardia: The sympathetic nervous system increases the heart rate to enhance cardiac output, ensuring that the existing red blood cells circulate through the systemic tissues more rapidly.
Step 3: Long-term Physiological Acclimatization
If the individual remains at high altitude, the body undergoes structural and biochemical adjustments to restore oxygen delivery efficiency:
| Mechanism | Biological Impact |
|---|---|
| Erythropoiesis | The kidneys release the hormone erythropoietin, stimulating bone marrow to produce more red blood cells, thereby increasing oxygen-carrying capacity. |
| Hemoglobin Affinity | Increased synthesis of $2,3-BPG$ (2,3-bisphosphoglycerate) shifts the oxygen-hemoglobin dissociation curve to the right, facilitating the unloading of $O_2$ at the tissue level. |
Visual Representation of Alveolar Gas Exchange
Step 4: Metabolic Consequences
The hyperventilation mentioned in Step 2 leads to a rapid "blowing off" of $CO_2$. This results in a state of respiratory alkalosis, where the blood $pH$ increases. The kidneys compensate for this over hours to days by excreting bicarbonate ($HCO_3^-$) ions into the urine to stabilize the $pH$ at normal physiological levels (approx. $7.4$).
Final Solution: Upon ascending a hill, the body experiences hypoxia due to reduced partial pressure of oxygen, triggering an immediate increase in the rate and depth of ventilation (hyperpnea) and heart rate, followed by long-term acclimatization via increased red blood cell production (erythropoiesis) and adjustments in hemoglobin-oxygen affinity.
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?
- Q4: What are the major transport mechanisms for $CO_2$? Explain.
- 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?
- 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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