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Breathing and Exchange of Gases – CBSE NCERT Study Resources

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11th

11th - Biology

Breathing and Exchange of Gases

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Overview of the Chapter

This chapter explores the process of breathing and exchange of gases in humans and other organisms. It covers the mechanisms of respiration, the structure and function of respiratory organs, and the transport of gases in the body. The chapter also discusses respiratory disorders and their impact on health.

Respiratory Organs

Different organisms have varied respiratory structures adapted to their environment:

  • Humans: Lungs are the primary respiratory organs.
  • Insects: Tracheal tubes facilitate gas exchange.
  • Fish: Gills are specialized for aquatic respiration.
  • Amphibians: Use skin, lungs, and buccal cavity for respiration.

Respiration: The biochemical process of releasing energy from organic molecules, primarily glucose, involving the intake of oxygen and release of carbon dioxide.

Human Respiratory System

The human respiratory system consists of:

  • Nostrils: Entry point for air.
  • Nasal cavity: Filters, warms, and humidifies air.
  • Pharynx: Common passage for air and food.
  • Larynx: Contains vocal cords and prevents food entry into the trachea.
  • Trachea: Windpipe lined with ciliated epithelium and cartilage rings.
  • Bronchi and Bronchioles: Branches of the trachea leading to alveoli.
  • Alveoli: Tiny air sacs where gas exchange occurs.

Mechanism of Breathing

Breathing involves two phases:

  • Inspiration: Active intake of air due to diaphragm contraction and rib cage expansion.
  • Expiration: Passive expulsion of air due to diaphragm relaxation and rib cage recoil.

Tidal Volume (TV): The volume of air inspired or expired during normal breathing (approx. 500 mL).

Exchange of Gases

Gas exchange occurs in alveoli and tissues via diffusion:

  • Oxygen diffuses from alveoli into blood.
  • Carbon dioxide diffuses from blood into alveoli.

Factors affecting diffusion:

  • Partial pressure gradient.
  • Surface area of respiratory membrane.
  • Thickness of the membrane.

Transport of Gases

Gases are transported in blood as follows:

  • Oxygen: Mostly bound to hemoglobin (97%) as oxyhemoglobin; a small amount dissolves in plasma.
  • Carbon dioxide: Transported as bicarbonate ions (70%), carbaminohemoglobin (23%), and dissolved in plasma (7%).

Respiratory Disorders

Common respiratory disorders include:

  • Asthma: Inflammation of airways causing breathing difficulty.
  • Emphysema: Alveolar damage reduces gas exchange efficiency.
  • Occupational Respiratory Disorders: Caused by inhaling harmful substances (e.g., silicosis, asbestosis).

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
Define respiration.
Answer:
Definition: The biochemical process of releasing energy from glucose in cells.
Question 2:
Name the primary respiratory organ in humans.
Answer:
Lungs
Question 3:
What is the role of hemoglobin in respiration?
Answer:
Transports oxygen from lungs to tissues and CO2 back.
Question 4:
Which muscle aids in breathing by contracting during inspiration?
Answer:
Diaphragm
Question 5:
What is the function of alveoli?
Answer:
Gas exchange between blood and air occurs here.
Question 6:
Name the respiratory pigment in human blood.
Answer:
Hemoglobin
Question 7:
What is tidal volume?
Answer:
Volume of air inhaled/exhaled during normal breathing (~500 mL).
Question 8:
Which gas is a byproduct of aerobic respiration?
Answer:
Carbon dioxide (CO2)
Question 9:
What prevents the collapse of trachea?
Answer:
C-shaped cartilaginous rings provide structural support.
Question 10:
Where does oxygen dissociation occur in the body?
Answer:
In tissues where oxygen is released from hemoglobin.
Question 11:
Name the enzyme that catalyzes CO2 + H2O reaction in RBCs.
Answer:
Carbonic anhydrase
Question 12:
What is the site of gaseous exchange in insects?
Answer:
Tracheal tubes directly deliver oxygen to tissues.
Question 13:
Name the primary site of gas exchange in humans.
Answer:

The alveoli in the lungs are the primary site of gas exchange due to their thin walls and rich capillary network.

Question 14:
State the volume of air remaining in the lungs after a forceful expiration.
Answer:

About 1100-1200 mL of air (residual volume) remains in the lungs to prevent alveolar collapse.

Question 15:
Differentiate between inspiration and expiration.
Answer:
  • Inspiration: Active process involving diaphragm contraction and rib expansion to inhale air.
  • Expiration: Usually passive due to diaphragm relaxation and elastic recoil of lungs.
Question 16:
Why does CO2 diffuse faster than O2 in blood?
Answer:

CO2 is 20 times more soluble in blood plasma than O2, enabling faster diffusion.

Question 17:
What is the function of epiglottis?
Answer:

The epiglottis is a flap that closes the trachea during swallowing to prevent food entry into the respiratory tract.

Question 18:
How does emphysema affect gas exchange?
Answer:

Emphysema damages alveolar walls, reducing surface area for gas exchange and causing shortness of breath.

Question 19:
Name the enzyme that facilitates CO2 transport in blood.
Answer:

Carbonic anhydrase in RBCs converts CO2 to bicarbonate ions for transport.

Question 20:
Why is the left lung smaller than the right?
Answer:

The left lung has a cardiac notch to accommodate the heart, making it slightly smaller.

Question 21:
List two protective mechanisms of the respiratory system.
Answer:
  • Mucus traps dust/pathogens.
  • Cilia sweep mucus away from the lungs.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Define respiration in humans.
Answer:

Respiration is the biochemical process where oxygen is used to break down glucose to release energy, and carbon dioxide is expelled as a waste product. It involves external respiration (gas exchange in lungs) and cellular respiration (energy production in cells).

Question 2:
Name the primary organs involved in external respiration.
Answer:

The primary organs are the lungs, where alveoli facilitate gas exchange between blood and air.

Question 3:
What is the role of hemoglobin in gas transport?
Answer:

Hemoglobin in RBCs binds oxygen to form oxyhemoglobin in lungs and releases it in tissues. It also carries carbon dioxide as carbaminohemoglobin.

Question 4:
How does diaphragm aid in breathing?
Answer:

The diaphragm contracts (flattens) during inspiration, increasing chest cavity volume, and relaxes (domes up) during expiration, decreasing volume.

Question 5:
Why are alveoli suited for gas exchange?
Answer:

Alveoli have:
1. Thin, moist walls for diffusion.
2. Large surface area.
3. Rich capillary network for efficient gas transport.

Question 6:
Explain the term vital capacity.
Answer:

Vital capacity is the maximum air volume exhaled after a deep inhalation (≈3.5–4.5 L). It includes tidal volume, inspiratory reserve volume, and expiratory reserve volume.

Question 7:
How is carbon dioxide transported in blood?
Answer:

CO2 is transported as:
1. Bicarbonate ions (70%).
2. Carbaminohemoglobin (23%).
3. Dissolved in plasma (7%).

Question 8:
What causes oxygen dissociation curve to shift right?
Answer:

The curve shifts right due to:
1. High CO2 (Bohr effect).
2. Low pH (acidic).
3. High temperature.
This indicates oxygen is released more readily to tissues.

Question 9:
State the function of epiglottis.
Answer:

The epiglottis is a flap that closes the trachea during swallowing to prevent food/liquid entry into lungs.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain the role of diaphragm and intercostal muscles in the process of breathing.
Answer:

The diaphragm and intercostal muscles play a crucial role in breathing by facilitating the expansion and contraction of the thoracic cavity.

During inhalation:

  • The diaphragm contracts and flattens, increasing the vertical space in the thoracic cavity.
  • The external intercostal muscles contract, lifting the ribs upward and outward, expanding the chest cavity.

During exhalation:
  • The diaphragm relaxes and returns to its dome shape, reducing the thoracic cavity's volume.
  • The internal intercostal muscles contract, pulling the ribs downward and inward, further decreasing space.

This coordinated movement creates pressure differences, allowing air to flow in and out of the lungs.

Question 2:
How does oxygen dissociation curve shift under high CO2 concentration? Explain with reason.
Answer:

The oxygen dissociation curve shifts to the right under high CO2 concentration, a phenomenon known as the Bohr effect.

Reasons:

  • Increased CO2 lowers blood pH (more acidic), reducing hemoglobin's affinity for oxygen.
  • This ensures oxygen is released more readily to tissues with high metabolic activity (like muscles during exercise).

This shift enhances oxygen delivery where it is most needed, improving efficiency of gas exchange.

Question 3:
Differentiate between inspiration and expiration based on muscle involvement and pressure changes.
Answer:

Inspiration:

  • Active process involving contraction of diaphragm and external intercostal muscles.
  • Thoracic volume increases, reducing intra-pulmonary pressure below atmospheric pressure, causing air inflow.

Expiration:
  • Mostly passive (except during forced exhalation), relying on relaxation of diaphragm and external intercostals.
  • Thoracic volume decreases, raising intra-pulmonary pressure above atmospheric pressure, forcing air out.
Question 4:
Why is alveoli considered the primary site of gas exchange? List two structural adaptations.
Answer:

The alveoli are the primary site of gas exchange due to their specialized structure:

  • Thin walls (single squamous epithelium) for rapid diffusion of gases.
  • Rich capillary network surrounding each alveolus ensures efficient oxygen uptake and CO2 removal.

Additionally, their large surface area (~70 m²) maximizes gas exchange capacity.

Question 5:
Describe the transport of CO2 in blood. Mention two forms.
Answer:

CO2 is transported in blood in three forms:

  • Dissolved in plasma (7-10%).
  • As bicarbonate ions (HCO3-) (70%), formed when CO2 reacts with water in RBCs (catalyzed by carbonic anhydrase).
  • Bound to hemoglobin as carbaminohemoglobin (20-25%).

This multi-pathway transport ensures efficient removal of CO2 from tissues to lungs.

Question 6:
What is the significance of residual volume in lungs? How does it differ from tidal volume?
Answer:

Residual volume (RV) is the air remaining in lungs after forced expiration (~1100-1200 mL). Its significance:

  • Prevents lung collapse by maintaining alveolar pressure.
  • Ensures continuous gas exchange between breaths.

Difference from tidal volume (TV):
  • TV (~500 mL) is the air inhaled/exhaled during normal breathing, while RV cannot be expelled voluntarily.
Question 7:
How does oxygen dissociation curve get affected by high pCO2 and low pH? Explain.
Answer:

High pCO2 and low pH (acidic conditions) shift the oxygen dissociation curve to the right, known as the Bohr effect.

1. Increased pCO2 lowers the affinity of hemoglobin for oxygen, promoting oxygen release in tissues.

2. Low pH (high H+ ions) stabilizes the deoxyhemoglobin state, further enhancing oxygen unloading.

This ensures efficient oxygen delivery to metabolically active tissues where CO2 and acid levels are high.

Question 8:
Describe the transport of carbon dioxide in the blood.
Answer:

Carbon dioxide is transported in three forms:

1. Dissolved in plasma (7-10%): CO2 is physically dissolved and carried as a gas.

2. As bicarbonate ions (70%): CO2 reacts with water in RBCs to form carbonic acid, which dissociates into H+ and HCO3- (bicarbonate).

3. Bound to hemoglobin (20-23%): CO2 binds to the globin part of hemoglobin, forming carbaminohemoglobin.

Question 9:
What is the significance of the residual volume in the lungs?
Answer:

Residual volume is the air remaining in the lungs after forceful expiration. Its significance includes:

1. Prevents lung collapse by maintaining slight inflation.

2. Ensures continuous gas exchange between breaths.

3. Stabilizes oxygen and CO2 levels in the blood during the breathing cycle.

Without it, alveoli would stick together, making re-inflation difficult.

Question 10:
Explain how emphysema affects the respiratory system.
Answer:

Emphysema is a chronic disorder where alveolar walls are damaged, reducing the lungs' surface area for gas exchange.

1. Loss of elasticity in alveoli leads to air trapping, making exhalation difficult.

2. Decreased oxygen diffusion causes breathlessness.

3. Often caused by smoking or pollution, it results in reduced respiratory efficiency and increased workload on breathing muscles.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the mechanism of breathing in humans with emphasis on inspiration and expiration.
Answer:
Theoretical Framework

We studied that breathing involves two phases: inspiration (inhaling) and expiration (exhaling). It is controlled by the diaphragm and intercostal muscles.

Evidence Analysis
  • During inspiration, the diaphragm contracts, increasing thoracic volume, lowering lung pressure, and drawing air in.
  • During expiration, the diaphragm relaxes, reducing thoracic volume, increasing lung pressure, and pushing air out.
Critical Evaluation

Our textbook shows that forced expiration involves abdominal muscles, unlike normal breathing. This highlights the adaptability of the respiratory system.

Future Implications

Understanding this mechanism helps in treating respiratory disorders like asthma, where muscle coordination is disrupted.

Question 2:
Describe the transport of oxygen and carbon dioxide in blood with reference to hemoglobin.
Answer:
Theoretical Framework

We learned that oxygen and carbon dioxide are transported via blood, primarily bound to hemoglobin or dissolved in plasma.

Evidence Analysis
  • Oxygen binds to hemoglobin as oxyhemoglobin (97%) or dissolves in plasma (3%).
  • Carbon dioxide is transported as bicarbonate (70%), carbaminohemoglobin (23%), or dissolved (7%).
Critical Evaluation

Our textbook highlights the Bohr effect, where CO2 lowers hemoglobin's oxygen affinity, ensuring efficient gas exchange.

Future Implications

This knowledge aids in treating hypoxia and CO2 retention disorders.

Question 3:
Compare aerobic and anaerobic respiration in terms of energy yield and byproducts.
Answer:
Theoretical Framework

We studied that aerobic respiration occurs with oxygen, while anaerobic respiration occurs without it, differing in energy yield and byproducts.

Evidence Analysis
  • Aerobic respiration yields 38 ATP, CO2, and H2O.
  • Anaerobic respiration yields 2 ATP and lactic acid (in humans) or ethanol (in yeast).
Critical Evaluation

Our textbook shows aerobic respiration is more efficient but requires oxygen, while anaerobic is a temporary solution during oxygen deficit.

Future Implications

This comparison explains muscle fatigue and fermentation processes in industries.

Question 4:
Explain the regulation of respiration by the respiratory centers in the brain.
Answer:
Theoretical Framework

We learned that respiration is regulated by respiratory centers in the medulla and pons, responding to CO2, O2, and pH levels.

Evidence Analysis
  • The medulla's rhythmicity area controls basic breathing rhythm.
  • The pons adjusts the rate and depth of breathing.
Critical Evaluation

Our textbook highlights chemoreceptors detecting blood CO2 levels, ensuring homeostasis. For example, high CO2 increases breathing rate.

Future Implications

Understanding this helps in managing conditions like sleep apnea, where regulatory mechanisms fail.

Question 5:
Discuss the disorders of the respiratory system with examples of asthma and emphysema.
Answer:
Theoretical Framework

We studied that respiratory disorders like asthma and emphysema impair gas exchange due to airway obstruction or alveolar damage.

Evidence Analysis
  • Asthma involves bronchial inflammation and constriction, causing wheezing.
  • Emphysema destroys alveoli, reducing lung elasticity and causing breathlessness.
Critical Evaluation

Our textbook shows asthma is often allergic, while emphysema is linked to smoking, highlighting preventable causes.

Future Implications

Early diagnosis and lifestyle changes can mitigate these disorders.

Question 6:
Describe the exchange of gases in alveoli and tissues, emphasizing partial pressure gradients.
Answer:
Theoretical Framework

We learned that gas exchange in alveoli and tissues relies on partial pressure gradients, driving diffusion of O2 and CO2.

Evidence Analysis
  • In alveoli, O2 diffuses from high (alveolar air) to low (blood) partial pressure.
  • In tissues, CO2 diffuses from high (tissue fluid) to low (blood) partial pressure.
Critical Evaluation

Our textbook highlights how gradients maximize efficiency, e.g., thin alveolar walls enhance diffusion.

Future Implications

This principle is vital for designing artificial respirators.

Question 7:
Explain the role of surfactant in reducing surface tension in the lungs.
Answer:
Theoretical Framework

We studied that surfactant, secreted by alveolar cells, reduces surface tension, preventing lung collapse.

Evidence Analysis
  • Surfactant disrupts water molecule cohesion, lowering surface tension.
  • This prevents alveolar collapse during expiration, especially in premature infants (respiratory distress syndrome).
Critical Evaluation

Our textbook shows surfactant deficiency increases breathing effort, proving its critical role.

Future Implications

Artificial surfactants are used to treat neonatal respiratory disorders.

Question 8:
Compare cutaneous, branchial, and pulmonary respiration with examples.
Answer:
Theoretical Framework

We learned that respiration occurs via cutaneous (skin), branchial (gills), or pulmonary (lungs) methods, varying by organism.

Evidence Analysis
  • Earthworms use cutaneous respiration due to moist skin.
  • Fish use branchial respiration with gills for water.
  • Humans use pulmonary respiration with lungs for air.
Critical Evaluation

Our textbook shows each method adapts to the environment, e.g., gills maximize surface area in water.

Future Implications

Studying these adaptations aids in evolutionary biology.

Question 9:
Analyze the effects of high altitude on respiration, including acclimatization.
Answer:
Theoretical Framework

We studied that high altitude reduces oxygen availability, triggering acclimatization responses like increased breathing rate.

Evidence Analysis
  • Initial symptoms include breathlessness and fatigue due to hypoxia.
  • Acclimatization involves increased RBC production and lung capacity over time.
Critical Evaluation

Our textbook shows athletes train at high altitudes to enhance performance, leveraging these adaptations.

Future Implications

Understanding this helps in managing altitude sickness in mountaineers.

Question 10:
Discuss the Haldane effect and its significance in CO2 transport.
Answer:
Theoretical Framework

We learned that the Haldane effect describes how oxygenated hemoglobin promotes CO2 release in tissues.

Evidence Analysis
  • In lungs, oxygen binding to hemoglobin reduces its affinity for CO2, releasing it.
  • In tissues, oxygen release increases hemoglobin's CO2 binding capacity.
Critical Evaluation

Our textbook highlights this as a key mechanism ensuring efficient CO2 removal and O2 delivery.

Future Implications

This principle is crucial in designing blood substitutes.

Question 11:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. How does this process ensure efficient gas exchange in the alveoli?
Answer:

The mechanism of breathing in humans involves two main phases: inspiration (inhalation) and expiration (exhalation). Both processes rely on the coordinated action of the diaphragm and intercostal muscles to change the volume and pressure in the thoracic cavity.

Inspiration:
1. The diaphragm contracts and flattens, increasing the vertical space in the thoracic cavity.
2. The external intercostal muscles contract, lifting the ribs and sternum upward and outward, expanding the chest cavity.
3. This increases lung volume, decreasing internal pressure, causing air to rush in.

Expiration:
1. The diaphragm relaxes and returns to its dome shape, reducing thoracic volume.
2. The internal intercostal muscles contract (during forced expiration), pulling ribs inward.
3. This decreases lung volume, increasing pressure, forcing air out.

Efficient Gas Exchange:
The alveoli are surrounded by capillaries where oxygen diffuses into the blood and carbon dioxide diffuses out. The breathing mechanism ensures:
1. Constant ventilation to maintain a steep concentration gradient.
2. Thin alveolar walls (one-cell thick) for rapid diffusion.
3. Large surface area of alveoli (~70m²) for maximum gas exchange.

Question 12:
Describe the transport of oxygen and carbon dioxide in the blood. Include the role of hemoglobin and the chloride shift phenomenon.
Answer:

Oxygen Transport:
1. Oxygen is carried in the blood primarily (97%) by hemoglobin in red blood cells as oxyhemoglobin (HbO2).
2. Hemoglobin has four heme groups, each binding one O2 molecule cooperatively.
3. A small amount (3%) dissolves directly in plasma.

Carbon Dioxide Transport:
1. Carbon dioxide is transported in three forms:
- 7% dissolved in plasma.
- 23% as carbaminohemoglobin (bound to hemoglobin).
- 70% as bicarbonate ions (HCO3-) in plasma.

Chloride Shift (Hamburger Phenomenon):
1. In tissues, CO2 diffuses into RBCs and converts to H2CO3 via carbonic anhydrase.
2. H2CO3 dissociates into H+ and HCO3-.
3. HCO3- moves out to plasma, and Cl- ions enter RBCs to maintain ionic balance.
4. Reverse occurs in lungs when CO2 is exhaled.

This efficient transport ensures:
- Oxygen delivery to tissues for cellular respiration.
- Removal of CO2, a metabolic waste, preventing acidosis.

Question 13:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. Also, discuss how the respiratory volume is measured.
Answer:

The mechanism of breathing in humans involves two main processes: inspiration (inhalation) and expiration (exhalation). These processes are primarily driven by the contraction and relaxation of the diaphragm and intercostal muscles.

Inspiration:
1. The diaphragm contracts and flattens, increasing the vertical volume of the thoracic cavity.
2. The external intercostal muscles contract, lifting the ribs and sternum upward and outward, expanding the thoracic cavity laterally.
3. This expansion reduces the intra-pulmonary pressure, causing air to rush into the lungs.

Expiration:
1. The diaphragm relaxes and returns to its dome shape, reducing the thoracic cavity's vertical volume.
2. The internal intercostal muscles contract (during forced expiration), pulling the ribs inward.
3. The thoracic cavity's volume decreases, increasing intra-pulmonary pressure, forcing air out of the lungs.

Measurement of Respiratory Volume:
Respiratory volumes are measured using a spirometer. Key measurements include:

  • Tidal Volume (TV): Normal breathing volume (~500 mL).
  • Inspiratory Reserve Volume (IRV): Additional air inhaled forcibly (~2500–3000 mL).
  • Expiratory Reserve Volume (ERV): Additional air exhaled forcibly (~1000–1100 mL).
  • Residual Volume (RV): Air remaining in lungs after forced expiration (~1100–1200 mL).
These volumes help assess lung function and diagnose respiratory disorders.

Question 14:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. Also, discuss how the volume and pressure changes in the thoracic cavity facilitate this process.
Answer:

The mechanism of breathing in humans involves two main phases: inspiration (inhalation) and expiration (exhalation). These processes are driven by the coordinated action of the diaphragm and intercostal muscles, along with changes in the thoracic cavity's volume and pressure.

Inspiration:
1. The diaphragm contracts and flattens, increasing the vertical length of the thoracic cavity.
2. The external intercostal muscles contract, lifting the ribs and sternum upward and outward, expanding the thoracic cavity laterally.
3. This increases the volume of the thoracic cavity, reducing the intra-pulmonary pressure below atmospheric pressure.
4. As a result, air rushes into the lungs to equalize the pressure.

Expiration:
1. The diaphragm relaxes and returns to its dome-shaped position, decreasing the thoracic cavity's vertical length.
2. The internal intercostal muscles contract (during forced expiration), pulling the ribs inward.
3. This reduces the thoracic cavity's volume, increasing the intra-pulmonary pressure above atmospheric pressure.
4. Air is expelled out of the lungs to balance the pressure.

Key Points:

  • The diaphragm is the primary muscle for breathing, while the intercostal muscles assist in rib movement.
  • Volume and pressure changes follow Boyle’s Law (pressure inversely proportional to volume).
  • During normal breathing, expiration is passive, but it becomes active during exercise or forced exhalation.

This mechanism ensures efficient gas exchange in the alveoli, maintaining oxygen supply and carbon dioxide removal.

Question 15:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. Also, discuss how the partial pressure gradient facilitates gaseous exchange in the alveoli.
Answer:

The mechanism of breathing in humans involves two main phases: inspiration (inhalation) and expiration (exhalation). These processes are driven by the coordinated action of the diaphragm and intercostal muscles.


Inspiration: During inhalation, the diaphragm contracts and flattens, while the external intercostal muscles lift the rib cage upward and outward. This increases the volume of the thoracic cavity, reducing the intra-pulmonary pressure below atmospheric pressure. As a result, air rushes into the lungs.


Expiration: During exhalation, the diaphragm relaxes and becomes dome-shaped, while the internal intercostal muscles (during forced expiration) pull the rib cage downward and inward. This decreases the thoracic cavity volume, increasing intra-pulmonary pressure above atmospheric pressure, forcing air out of the lungs.


The partial pressure gradient plays a crucial role in gaseous exchange in the alveoli. Oxygen (O2) diffuses from the alveoli (high pO2) into the blood (low pO2), while carbon dioxide (CO2) diffuses from the blood (high pCO2) into the alveoli (low pCO2). This gradient ensures efficient gas exchange to meet metabolic demands.


Additionally, the large surface area of alveoli, thin respiratory membrane, and presence of surfactant further enhance gas exchange efficiency.

Question 16:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. Also, discuss how the respiratory volumes are affected during vigorous exercise.
Answer:

The mechanism of breathing in humans involves two main phases: inspiration (inhalation) and expiration (exhalation). Both processes are driven by the coordinated action of the diaphragm and intercostal muscles.


Inspiration: During inhalation, the diaphragm contracts and flattens, while the external intercostal muscles lift the ribcage upward and outward. This increases the thoracic cavity volume, reducing lung pressure below atmospheric pressure, causing air to rush in.


Expiration: During exhalation, the diaphragm relaxes and domes upward, while the internal intercostal muscles (during forced expiration) pull the ribcage downward. This decreases thoracic volume, increasing lung pressure above atmospheric pressure, forcing air out.


Respiratory Volumes During Exercise: Vigorous exercise significantly alters respiratory volumes:

  • Tidal Volume (TV): Increases to allow more air per breath.
  • Inspiratory Reserve Volume (IRV): Decreases as more air is inhaled actively.
  • Expiratory Reserve Volume (ERV): Decreases due to forceful exhalation.
  • Vital Capacity (VC): Remains unchanged but is utilized more efficiently.

Additionally, residual volume stays constant, while minute ventilation (TV × breathing rate) rises sharply to meet oxygen demand and remove excess CO2.

Question 17:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. Also, discuss how the volume and pressure changes in the thoracic cavity facilitate this process.
Answer:

The mechanism of breathing in humans involves two main phases: inspiration (inhalation) and expiration (exhalation). These processes are primarily driven by the contraction and relaxation of the diaphragm and intercostal muscles, leading to changes in the volume and pressure of the thoracic cavity.

Inspiration:
1. The diaphragm contracts and flattens, moving downward.
2. The external intercostal muscles contract, lifting the ribs upward and outward.
3. These actions increase the volume of the thoracic cavity.
4. As volume increases, the pressure inside the lungs decreases (Boyle's Law).
5. Air rushes into the lungs from the higher atmospheric pressure outside to equalize the pressure.

Expiration:
1. The diaphragm relaxes and returns to its dome-shaped position.
2. The external intercostal muscles relax, allowing the ribs to move downward and inward.
3. These actions decrease the volume of the thoracic cavity.
4. As volume decreases, the pressure inside the lungs increases.
5. Air is forced out of the lungs to the lower atmospheric pressure outside.

The thoracic cavity acts like a pump, with volume and pressure changes ensuring efficient gas exchange. During intense activity, abdominal muscles and internal intercostal muscles assist in forceful exhalation.

Question 18:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. How does this process ensure efficient gas exchange in the alveoli?
Answer:

The mechanism of breathing in humans involves two main phases: inspiration (inhalation) and expiration (exhalation). Both processes rely on the coordinated action of the diaphragm and intercostal muscles to change the volume and pressure within the thoracic cavity.


Inspiration: During inhalation, the diaphragm contracts and flattens, while the external intercostal muscles lift the ribcage upward and outward. This increases the thoracic volume, reducing lung pressure below atmospheric pressure, causing air to rush into the lungs.


Expiration: During exhalation, the diaphragm relaxes and domes upward, while the internal intercostal muscles (during forced expiration) pull the ribcage downward. This decreases thoracic volume, increasing lung pressure above atmospheric pressure, forcing air out.


The efficiency of gas exchange in the alveoli is ensured by:

  • Large surface area due to millions of alveoli.
  • Thin alveolar walls (single-cell layer) for rapid diffusion.
  • Rich capillary network maintaining a steep concentration gradient.
  • Surfactant reducing surface tension, preventing alveolar collapse.


This mechanism maintains optimal oxygen supply for cellular respiration and removes carbon dioxide, a metabolic waste product, ensuring homeostasis.

Question 19:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. Also, discuss how the respiratory volume is measured using a spirometer.
Answer:

The mechanism of breathing in humans involves two main processes: inspiration (inhaling) and expiration (exhaling). These processes are driven by the coordinated action of the diaphragm and intercostal muscles.


Inspiration: During inhalation, the diaphragm contracts and flattens, while the external intercostal muscles lift the rib cage upward and outward. This increases the volume of the thoracic cavity, reducing lung pressure and allowing air to rush in.


Expiration: During exhalation, the diaphragm relaxes and domes upward, while the internal intercostal muscles pull the rib cage downward and inward. This decreases thoracic volume, increasing lung pressure and forcing air out.


Respiratory volumes are measured using a spirometer, which records the amount of air inhaled or exhaled. Key measurements include:

  • Tidal Volume (TV): Normal breathing volume (~500 mL).
  • Inspiratory Reserve Volume (IRV): Extra air inhaled forcefully (~2500–3000 mL).
  • Expiratory Reserve Volume (ERV): Extra air exhaled forcefully (~1000–1100 mL).
  • Residual Volume (RV): Air remaining after forceful exhalation (~1100–1200 mL).

These volumes help assess lung function and diagnose respiratory disorders.

Question 20:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. Also, discuss how the respiratory volume is measured using a spirometer.
Answer:

The mechanism of breathing in humans involves two main processes: inspiration (inhalation) and expiration (exhalation). These processes are facilitated by the coordinated action of the diaphragm and intercostal muscles.

Inspiration:
1. The diaphragm contracts and flattens, increasing the vertical volume of the thoracic cavity.
2. The external intercostal muscles contract, lifting the ribs and sternum upward and outward, further expanding the thoracic cavity.
3. This expansion reduces the intra-pulmonary pressure, causing air to rush into the lungs.

Expiration:
1. The diaphragm relaxes and returns to its dome-shaped position, reducing the thoracic cavity's vertical volume.
2. The internal intercostal muscles contract, pulling the ribs and sternum downward and inward.
3. This decreases the thoracic cavity's volume, increasing intra-pulmonary pressure, and forcing air out of the lungs.

Measurement of Respiratory Volume using Spirometer:
A spirometer is a device used to measure the volume of air inhaled and exhaled by the lungs. Key measurements include:
1. Tidal Volume (TV): The volume of air inhaled or exhaled during normal breathing (approx. 500 mL).
2. Inspiratory Reserve Volume (IRV): Additional air inhaled forcefully after a normal inspiration (approx. 2500-3000 mL).
3. Expiratory Reserve Volume (ERV): Additional air exhaled forcefully after a normal expiration (approx. 1000-1100 mL).
4. Residual Volume (RV): Air remaining in the lungs after forceful expiration (approx. 1100-1200 mL).
5. Vital Capacity (VC): The maximum air exhaled after a maximum inspiration (TV + IRV + ERV).

Understanding these mechanisms and measurements is crucial for diagnosing respiratory disorders and assessing lung function.

Question 21:
Explain the mechanism of breathing in humans with emphasis on the role of diaphragm and intercostal muscles. How does this process ensure efficient gas exchange in the alveoli?
Answer:

The mechanism of breathing in humans involves two main phases: inspiration (inhalation) and expiration (exhalation). Both processes rely on the coordinated action of the diaphragm and intercostal muscles to change the volume and pressure within the thoracic cavity.


Inspiration: During inhalation, the diaphragm contracts and flattens, while the external intercostal muscles lift the rib cage upward and outward. This increases the thoracic volume, reducing lung pressure below atmospheric pressure, causing air to rush in.


Expiration: During exhalation, the diaphragm relaxes and domes upward, while the internal intercostal muscles (during forced expiration) pull the ribs downward. This decreases thoracic volume, increasing lung pressure above atmospheric pressure, forcing air out.


Efficient gas exchange in the alveoli is ensured by:

  • Large surface area due to millions of alveoli.
  • Thin walls (single-cell layer) for rapid diffusion.
  • Rich blood supply via capillaries maintaining a steep concentration gradient.
  • Surfactant reducing surface tension, preventing alveolar collapse.

Question 22:
Describe the transport of oxygen and carbon dioxide in the blood. Include the role of hemoglobin, carbonic anhydrase, and the chloride shift in your answer.
Answer:

Oxygen Transport: Oxygen is primarily transported bound to hemoglobin (Hb) in red blood cells, forming oxyhemoglobin (HbO2). Each Hb molecule binds 4 O2 molecules. A small amount dissolves directly in plasma.


Carbon Dioxide Transport: CO2 is transported in three forms:

  • As bicarbonate ions (70%)—CO2 reacts with water in RBCs, catalyzed by carbonic anhydrase, forming H2CO3, which dissociates into H+ and HCO3−.
  • Bound to Hb as carbaminohemoglobin (23%).
  • Dissolved in plasma (7%).


The chloride shift maintains ionic balance: HCO3− diffuses out of RBCs into plasma, while Cl− moves in (to prevent charge imbalance). This ensures efficient CO2 transport without altering blood pH drastically.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A patient with chronic bronchitis has reduced alveolar ventilation. Analyze how this condition affects oxygen diffusion and carbon dioxide elimination.
Answer:
Case Deconstruction

Chronic bronchitis causes inflammation of bronchial tubes, narrowing airways and reducing airflow. This lowers alveolar ventilation, limiting gas exchange.

Theoretical Application
  • Reduced oxygen diffusion: Less air reaches alveoli, decreasing O2 partial pressure gradient.
  • Impaired CO2 elimination: CO2 accumulates due to slower exhalation, raising blood acidity.
Critical Evaluation

Our textbook shows similar cases where mucus plugs further block airways, worsening hypoxia. Example: Smokers often exhibit these symptoms due to cilia damage.

Question 2:
Compare tidal volume and vital capacity in an athlete versus a sedentary individual. Justify with physiological adaptations.
Answer:
Case Deconstruction

Athletes have higher lung efficiency due to training. We studied how exercise strengthens respiratory muscles.

Theoretical Application
  • Tidal volume: Athletes inhale 600-700 mL/breath vs. 500 mL in sedentary people.
  • Vital capacity: Athletes reach 4.5-5L due to expanded alveoli, while others average 3-4L.
Critical Evaluation

Example: Swimmers show 20% higher vital capacity from diaphragmatic training. Our textbook links this to increased red blood cell production.

Question 3:
How does altitude sickness disrupt oxygen-hemoglobin dissociation? Propose two compensatory mechanisms.
Answer:
Case Deconstruction

At high altitudes, low O2 pressure reduces hemoglobin saturation. We studied this in the oxygen-hemoglobin curve.

Theoretical Application
  • Disruption: O2-Hb dissociation shifts left, impairing O2 release to tissues.
  • Compensation: Increased RBC production and faster breathing rate.
Critical Evaluation

Example: Mountaineers use acclimatization to trigger erythropoietin. Textbook data shows 2,3-DPG rise aids O2 unloading.

Question 4:
A graph shows CO2 transport drops when carbonic anhydrase is inhibited. Explain the biochemical pathway affected and its systemic impact.
Answer:
Case Deconstruction

Carbonic anhydrase accelerates CO2 conversion to bicarbonate in RBCs. Inhibition stalls this reaction.

Theoretical Application
  • Pathway: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- slows.
  • Impact: Blood pH rises (alkalosis), reducing respiratory drive.
Critical Evaluation

Example: Diuretics like acetazolamide cause this effect. Textbook confirms it disrupts chloride shift, lowering CO2 transport by 70%.

Question 5:
During a lab experiment, students observed that hemoglobin binds more efficiently to oxygen in the lungs but releases it readily in tissues. Explain this phenomenon using oxygen dissociation curve and Bohr effect.
Answer:
Case Deconstruction

We studied that hemoglobin's affinity for oxygen varies with conditions. In lungs, high pO2 and low pCO2 promote oxygen binding.

Theoretical Application
  • The oxygen dissociation curve shifts left in lungs due to low H+ concentration.
  • In tissues, Bohr effect lowers affinity due to high CO2 and acidity.
Critical Evaluation

Our textbook shows this adaptation ensures oxygen delivery where needed, like in muscles during exercise.

Question 6:
A patient with emphysema struggles with exhaling air. Analyze how this affects residual volume and vital capacity, referencing lung anatomy.
Answer:
Case Deconstruction

We learned emphysema damages alveoli walls, reducing elastic recoil.

Theoretical Application
  • Residual volume increases as trapped air cannot be expelled.
  • Vital capacity decreases due to loss of alveolar surface area.
Critical Evaluation

Our textbook shows this matches clinical data where patients exhibit barrel-shaped chests from air retention.

Question 7:
Compare chloride shift and Hamburger phenomenon in RBCs during gas exchange. Use examples from pulmonary and systemic capillaries.
Answer:
Case Deconstruction

Both processes maintain ionic balance during CO2 transport. We studied them in Chapter 17.

Theoretical Application
  • Chloride shift: Cl- enters RBCs as HCO3- leaves in tissues.
  • Hamburger phenomenon: Reverse occurs in lungs when HCO3- re-enters.
Critical Evaluation

This explains why RBCs swell slightly in tissues and shrink in lungs, as per our lab observations.

Question 8:
A mountaineer experiences altitude sickness due to low atmospheric pressure. Explain the body's acclimatization mechanisms involving erythropoietin and breathing rate.
Answer:
Case Deconstruction

We studied that low pO2 triggers physiological adaptations.

Theoretical Application
  • Kidneys release erythropoietin to increase RBC production.
  • Chemoreceptors raise breathing rate to enhance oxygen uptake.
Critical Evaluation

Our textbook shows these changes take 2-3 weeks, explaining why climbers ascend gradually, like in Everest expeditions.

Question 9:
A patient with chronic bronchitis exhibits reduced FEV1/FVC ratio and dyspnea. Analyze the physiological basis of these symptoms and explain how alveolar ventilation is affected.
Answer:
Case Deconstruction

Chronic bronchitis causes airway inflammation, narrowing bronchioles and increasing mucus production. This obstructs airflow, reducing FEV1 (forced expiratory volume) while FVC (forced vital capacity) remains less affected, lowering the FEV1/FVC ratio.

Theoretical Application
  • Dyspnea occurs due to increased effort to overcome airway resistance.
  • Alveolar ventilation decreases as trapped air reduces fresh oxygen exchange, leading to hypoxemia.
Critical Evaluation

Our textbook shows similar cases where COPD patients struggle with gas exchange. Example: Emphysema also reduces FEV1 but via alveolar wall destruction.

Question 10:
Compare oxyhemoglobin dissociation curves at high-altitude versus sea level. How does Bohr’s effect influence oxygen delivery during exercise?
Answer:
Case Deconstruction

At high altitude, lower pO2 shifts the curve right, enhancing oxygen unloading. At sea level, higher pO2 favors oxygen loading.

Theoretical Application
  • Bohr’s effect: Increased CO2 and acidity during exercise further shift the curve right, releasing more O2 to tissues.
  • Example: Athletes training in mountains adapt via elevated 2,3-DPG.
Critical Evaluation

We studied how fetal hemoglobin’s left-shifted curve contrasts with adult curves, prioritizing O2 uptake in low-pO2 environments.

Question 11:
A diver experiences nitrogen narcosis at 30m depth. Link this to Henry’s law and propose why helium-oxygen mixes are safer for deep dives.
Answer:
Case Deconstruction

At high pressure, nitrogen dissolves excessively in blood (per Henry’s law), impairing neuron function and causing narcosis.

Theoretical Application
  • Helium’s lower solubility reduces narcosis risk.
  • Example: Commercial divers use Trimix (He/O2/N2) to limit nitrogen exposure.
Critical Evaluation

Our textbook highlights decompression sickness as another pressure-related hazard, where rapid ascent forms nitrogen bubbles in tissues.

Question 12:
Explain how asthma alters airway resistance and lung compliance. Contrast this with pulmonary fibrosis using a pressure-volume curve.
Answer:
Case Deconstruction

Asthma increases resistance via bronchoconstriction but doesn’t significantly reduce compliance. Fibrosis stiffens lungs, lowering compliance.

Theoretical Application
  • Pressure-volume curve: Asthma shows normal slope (compliance), while fibrosis has a flatter curve (reduced compliance).
  • Example: Inhalers relieve asthma by dilating airways, but fibrosis lacks such targeted treatment.
Critical Evaluation

We studied how smoking-induced emphysema increases compliance, contrasting fibrosis’s restrictive pattern.

Question 13:

Rahul, a 11th-grade student, observed that his breathing rate increased significantly after running a 100-meter race. His teacher explained that this was due to the increased demand for oxygen in his body.

a) Identify the respiratory center in the brain responsible for regulating breathing rate.
b) Explain how the levels of carbon dioxide and oxygen in the blood influence this center.
c) Why does Rahul's breathing rate remain elevated for some time even after stopping the race?

Answer:

a) The respiratory center is located in the medulla oblongata of the brain, which regulates the rate and depth of breathing.

b)

  • Increased carbon dioxide (CO2) levels in the blood lower the pH, detected by chemoreceptors in the medulla and aortic/carotid bodies.
  • This triggers the respiratory center to increase breathing rate to expel excess CO2.
  • Low oxygen (O2) levels also stimulate peripheral chemoreceptors, but CO2 is the primary regulator.

c) Rahul's breathing rate remains elevated post-race because:
1. Oxygen debt needs to be repaid—his body requires extra O2 to metabolize accumulated lactic acid.
2. CO2 levels take time to normalize after intense activity.

Question 14:

Priya conducted an experiment where she compared the breathing rates of a person at rest and after climbing stairs. She noted differences in tidal volume and respiratory rate.

a) Define tidal volume and vital capacity.
b) How do these values change during exercise?
c) What role do intercostal muscles and the diaphragm play in this process?

Answer:

a)

  • Tidal volume: Volume of air inhaled/exhaled normally during rest (~500 mL).
  • Vital capacity: Maximum air expelled after a deep inhalation (includes tidal + inspiratory/expiratory reserve volumes).

b) During exercise:
1. Tidal volume increases (up to 3-4 times) to meet oxygen demand.
2. Respiratory rate rises to enhance gas exchange efficiency.

c)

  • External intercostal muscles contract more forcefully to elevate ribs, expanding the thoracic cavity.
  • The diaphragm contracts more deeply, further increasing lung volume.
  • Together, they reduce intra-pulmonary pressure, allowing faster air intake.

Question 15:

Rahul, a 11th-grade student, was curious about the mechanism of breathing during his biology class. His teacher explained that the process involves the movement of the diaphragm and intercostal muscles. Based on this, answer the following:

  • Describe the role of the diaphragm and intercostal muscles during inhalation and exhalation.
  • How does the thoracic cavity volume change during these processes?
Answer:

Role of Diaphragm and Intercostal Muscles:
During inhalation, the diaphragm contracts and flattens, while the external intercostal muscles contract, lifting the ribs upward and outward.
During exhalation, the diaphragm relaxes and becomes dome-shaped, while the internal intercostal muscles contract, pulling the ribs downward and inward.

Change in Thoracic Cavity Volume:
During inhalation, the thoracic cavity volume increases, reducing lung pressure and allowing air to rush in.
During exhalation, the thoracic cavity volume decreases, increasing lung pressure and forcing air out.

Additional Note: This mechanism is part of negative pressure breathing, where pressure differences drive air movement.

Question 16:

Priya observed that her breathing rate increased after running. She wondered how the body regulates this change. Answer the following:

  • Name the respiratory center in the brain responsible for controlling breathing rate.
  • Explain how CO2 concentration in the blood influences this center.
  • Why does the breathing rate increase during exercise?
Answer:

Respiratory Center:
The medulla oblongata and pons in the brainstem form the respiratory center that controls breathing rate.

Role of CO2:
An increase in CO2 concentration lowers blood pH, detected by chemoreceptors. These send signals to the respiratory center to increase breathing rate, removing excess CO2.

Exercise and Breathing Rate:
During exercise, muscle activity produces more CO2, which triggers the respiratory center to increase breathing rate for faster gas exchange.

Additional Note: This is part of homeostasis, where the body maintains internal balance.

Question 17:

Rahul, a 11th-grade student, was studying the mechanism of breathing. His teacher explained that during inspiration, the diaphragm contracts and flattens, increasing the volume of the thoracic cavity. However, Rahul wondered how this change in volume leads to air entering the lungs. Explain the process step-by-step, including the role of pressure gradients and muscles involved.

Answer:

During inspiration, the following steps occur:


1. The diaphragm contracts and flattens, while the external intercostal muscles lift the rib cage upward and outward.
2. This increases the volume of the thoracic cavity, reducing the intrapulmonary pressure (pressure inside the lungs).
3. As the pressure inside the lungs becomes lower than the atmospheric pressure, air rushes in to equalize the pressure gradient.
4. The alveoli expand to accommodate the incoming air, facilitating gas exchange.


Additional Insight: The process is passive during normal exhalation, as the muscles relax and the elastic recoil of the lungs pushes air out.

Question 18:

Priya observed that mountaineers often carry oxygen cylinders while climbing high altitudes. She learned that at high altitudes, the air has less oxygen partial pressure, making breathing difficult. Explain how the human body initially responds to low oxygen levels, including the role of chemoreceptors and the respiratory center in the brain.

Answer:

At high altitudes, the body responds to low oxygen levels as follows:


1. Chemoreceptors (located in the aortic arch and carotid bodies) detect the drop in oxygen partial pressure (hypoxia).
2. These receptors send signals to the respiratory center in the medulla oblongata.
3. The respiratory center increases the breathing rate (hyperventilation) to intake more oxygen.
4. The heart rate also increases temporarily to pump oxygen-rich blood faster.


Additional Insight: Prolonged exposure leads to acclimatization, where the body produces more RBCs to enhance oxygen transport.

Question 19:

Rahul, a 11th-grade student, was participating in a marathon. After the race, he experienced rapid breathing and muscle cramps. His friend suggested it was due to oxygen debt and accumulation of lactic acid.

(a) Explain the term oxygen debt and its connection to Rahul's condition.

(b) How does the body compensate for oxygen debt after intense exercise?

Answer:

(a) Oxygen debt refers to the extra oxygen required by the body after intense physical activity to break down accumulated lactic acid and restore energy reserves. During Rahul's marathon, his muscles worked anaerobically due to insufficient oxygen supply, leading to lactic acid buildup, which caused muscle cramps.


(b) The body compensates for oxygen debt by:

  • Increasing breathing rate (hyperventilation) to intake more oxygen.
  • Converting lactic acid back into pyruvate, which enters the Krebs cycle for aerobic respiration.
  • Replenishing ATP and creatine phosphate stores in muscles.
This process continues until oxygen levels return to normal, and all lactic acid is metabolized.

Question 20:

During a biology practical, students observed the effect of carbon monoxide (CO) on hemoglobin using a simulation. They noted that CO binds to hemoglobin more strongly than oxygen.

(a) Why is CO binding to hemoglobin dangerous for humans?

(b) How does this affect oxygen transport in the body?

Answer:

(a) Carbon monoxide (CO) binds to hemoglobin with an affinity 200 times greater than oxygen, forming carboxyhemoglobin. This reduces hemoglobin's oxygen-carrying capacity, leading to hypoxia (oxygen deficiency in tissues), which can be fatal.


(b) The effects on oxygen transport include:

  • Hemoglobin cannot bind oxygen efficiently, reducing oxygen delivery to cells.
  • Tissues and organs (especially the brain and heart) suffer from oxygen deprivation.
  • The oxygen dissociation curve shifts left, making hemoglobin less likely to release oxygen to tissues.
This condition is life-threatening and requires immediate medical intervention.

Question 21:
A group of students conducted an experiment to study the effect of high altitude on human respiration. They observed that individuals at higher altitudes experienced shortness of breath and increased respiratory rate. Based on this case, explain the physiological changes that occur in the respiratory system at high altitudes and how the body adapts to such conditions.
Answer:

At high altitudes, the partial pressure of oxygen (PO2) decreases due to lower atmospheric pressure. This leads to hypoxia (oxygen deficiency), causing the observed symptoms like shortness of breath and increased respiratory rate.

The body adapts through the following mechanisms:

  • Increased ventilation: The respiratory center in the medulla detects low oxygen levels and stimulates faster and deeper breathing to intake more oxygen.
  • Polycythemia: The kidneys release erythropoietin (EPO), which increases RBC production to enhance oxygen-carrying capacity.
  • Higher 2,3-DPG levels: This compound in RBCs reduces hemoglobin's affinity for oxygen, promoting its release to tissues.

Over time, these adaptations improve oxygen delivery, but immediate effects like altitude sickness may still occur.

Question 22:
A patient was diagnosed with emphysema, a chronic respiratory disorder. The doctor explained that the patient's alveoli were damaged, reducing the surface area for gas exchange. Using this case, describe how emphysema affects the process of breathing and gas exchange, and suggest one lifestyle change to manage the condition.
Answer:

In emphysema, the alveolar walls are destroyed, leading to:

  • Reduced surface area: Fewer alveoli mean less space for oxygen diffusion into the blood and CO2 removal.
  • Loss of elasticity: Damaged lung tissue cannot recoil properly, causing air trapping and difficulty exhaling.

This results in shortness of breath, chronic cough, and reduced oxygen supply to tissues.

A key lifestyle change is quitting smoking, as it is the primary cause of emphysema. Avoiding smoke and pollutants also slows disease progression.

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