Breathing and Exchange of Gases (NCERT Practice Paper)

Q1. Which disorder is characterized by inflammation of bronchi and bronchioles causing wheezing?

Correct Answer: (b)
Asthma is a chronic inflammatory condition of the airways. The inflammation leads to narrowing, mucus production, and wheezing, making breathing difficult.

Q2. The enzyme required for the transport of CO2 as bicarbonate is:

Correct Answer: (b)
Carbonic anhydrase, present in red blood cells, catalyzes the reversible hydration of CO2 to carbonic acid, which then dissociates into bicarbonate and hydrogen ions. This enzyme is essential for efficient CO2 transport.

Q3. Assertion: Alveoli are the primary sites of exchange of gases. Reason: They are irregular-walled and vascularised bag-like structures.

Correct Answer: (a)
Alveoli are the main sites of gas exchange because of their large surface area, thin walls, and dense capillary network. The reason describes these structural features, which directly enable efficient diffusion.

Q4. Match the partial pressure of CO2 (pCO2) with the site (Table 14.1):

Column-I (Site)	Column-II (pCO2 in mm Hg)
A. Atmospheric Air	(I) 40
B. Alveoli	(II) 45
C. Deoxygenated Blood	(III) 0.3
D. Tissues	(IV) 45

Correct Answer: (a)
Atmospheric pCO2 is 0.3 mm Hg; alveolar pCO2 is 40 mm Hg; deoxygenated blood and tissues both have about 45 mm Hg. These differences facilitate CO2 elimination.

Q5. Which of the following is true for 'Solubility'?
(i) CO2 is more soluble than O2.
(ii) Solubility is 20-25 times higher.
(iii) This increases CO2 diffusion rate across membranes.

Correct Answer: (a)
CO2 is 20–25 times more soluble than O2, and this higher solubility enhances its diffusion across respiratory membranes. All statements are correct.

Q6. Match the CO2 transport form with amount:

State	Percentage
A. Bicarbonate	(I) 7%
B. Carbamino-haemoglobin	(II) 70%
C. Dissolved in plasma	(III) 20-25%

Correct Answer: (a)
CO2 is transported mainly as bicarbonate (70%), about 20–25% as carbamino-haemoglobin, and only 7% dissolved in plasma.

Q7. During swallowing, the entry of food into the larynx is prevented by a thin elastic cartilaginous flap called:

Correct Answer: (b)
The epiglottis acts as a lid over the glottis (the opening of the larynx). When swallowing, it folds backward to cover the glottis, directing food into the esophagus and preventing aspiration into the airway.

Q8. The Italian anatomist Alfonso Corti began his scientific career studying which system in reptiles?

Correct Answer: (b)
Alfonso Corti initially researched the cardiovascular systems of reptiles. Later, he became famous for describing the organ of Corti in the cochlea, but his early work focused on the circulatory system of reptiles.

Q9. Select correct statements for 'Regulation of Respiration':
(i) Respiratory rhythm centre is in medulla.
(ii) Pneumotaxic centre is in pons.
(iii) O2 has a major role in regulation.

Correct Answer: (a)
The rhythm centre is in the medulla and the pneumotaxic centre in the pons; however, O2 plays a minor role in regulation compared to CO2 and H+. So (i) and (ii) are correct.

Q10. Match the respiratory volumes with their average values:

Column-I (Volume)	Column-II (Value in mL)
A. Tidal Volume	(I) 2500 – 3000
B. Inspiratory Reserve Volume	(II) 1100 – 1200
C. Expiratory Reserve Volume	(III) 500
D. Residual Volume	(IV) 1000 – 1100

Correct Answer: (a)
TV is 500 mL; IRV is 2500–3000 mL; ERV is 1000–1100 mL; and RV is 1100–1200 mL. These values represent typical static lung volumes.

Q11. Regarding 'Pleura', which is true?
(i) Double layered membrane covering lungs.
(ii) Contains pleural fluid.
(iii) Outer layer in contact with thoracic lining.

Correct Answer: (a)
The pleura is a double‑layered membrane; it contains pleural fluid for lubrication; and the outer (parietal) layer lines the thoracic cavity. All are true.

Q12. Which statements about 'CO2 Transport' are correct?
(i) 70% as bicarbonate.
(ii) 20-25% by RBCs.
(iii) 7% dissolved in plasma.

Correct Answer: (a)
CO2 transport distribution: 70% as bicarbonate, 20–25% as carbamino‑haemoglobin (RBCs), and 7% dissolved in plasma. All are correct.

Q13. Inspiration occurs when there is a ______ pressure in the lungs with respect to atmospheric pressure.

Correct Answer: (b)
During inspiration, the lungs expand, creating a sub-atmospheric (negative) pressure inside. Air flows from higher atmospheric pressure into the lungs to equalize the pressure gradient.

Q14. Branchial respiration refers to the use of:

Correct Answer: (c)
Branchial respiration involves gas exchange across gills, which are specialized outgrowths with a large surface area and rich blood supply. This is typical of aquatic animals like fishes and some amphibians.

Q15. What percentage of O2 is transported by RBCs in the blood?

Correct Answer: (d)
About 97% of oxygen in blood is carried bound to haemoglobin within red blood cells as oxyhaemoglobin. The remaining 3% is dissolved in plasma.

Q16. Assertion: Expiration occurs when intra-pulmonary pressure is higher than atmospheric pressure. Reason: Relaxation of the diaphragm and intercostal muscles reduces thoracic volume.

Correct Answer: (a)
During expiration, muscle relaxation decreases thoracic volume, increasing intra-pulmonary pressure above atmospheric, forcing air out. The reason correctly explains the pressure change.

Q17. Assertion: The conducting part clears the air from foreign particles. Reason: It includes the nostrils up to the terminal bronchioles.

Correct Answer: (b)
The conducting part does clean air, but the reason merely lists its components, not how cleansing occurs (via mucus and cilia). So both are true, but the reason is not the explanation.

Q18. Match the brain center with its location:

Column-I (Center)	Column-II (Location)
A. Respiratory rhythm centre	(I) Pons
B. Pneumotaxic centre	(II) Medulla
C. Receptors for CO2/H+	(III) Aortic arch

Correct Answer: (a)
The rhythm centre is in the medulla; the pneumotaxic centre is in the pons; and peripheral chemoreceptors sensitive to CO2/H+ are located in the aortic arch and carotid bodies.

Q19. Which are correct for 'Larynx'?
(i) Cartilaginous box.
(ii) Helps in sound production.
(iii) Called the sound box.

Correct Answer: (a)
The larynx is a cartilaginous structure that houses vocal cords, producing sound; it is often referred to as the sound box. All statements are correct.

Q20. Identify the correct features of the 'Diffusion Membrane':
(i) Thin squamous epithelium of alveoli.
(ii) Endothelium of alveolar capillaries.
(iii) Total thickness is much less than a millimetre.

Correct Answer: (a)
The diffusion membrane comprises alveolar epithelium, capillary endothelium, and a basement membrane; its total thickness is under 1 mm. All statements are correct.

Q21. Assertion: Trachea is supported by incomplete cartilaginous rings. Reason: It prevents the trachea from collapsing.

Correct Answer: (a)
The trachea has C‑shaped cartilage rings that maintain its patency and prevent collapse during pressure changes. The reason correctly explains the functional significance of the rings.

Q22. The partial pressure of CO2 (pCO2) in deoxygenated blood is:

Correct Answer: (b)
Deoxygenated blood returning from tissues has a pCO2 of about 45 mm Hg. This is higher than alveolar pCO2 (40 mm Hg), driving CO2 diffusion from blood into the alveoli.

Q23. Regarding 'Expiratory Reserve Volume' (ERV):
(i) Additional volume of air a person can expire forcibly.
(ii) Average 1000 to 1100 mL.
(iii) It is always larger than IRV.

Correct Answer: (a)
ERV is the extra air expired forcefully after a normal breath; its average is 1000–1100 mL. However, IRV (2500–3000 mL) is larger, so (iii) is false. Thus (i) and (ii) are correct.

Q24. Which of the following describes 'Asthma' correctly?
(i) Difficulty in breathing.
(ii) Causes wheezing.
(iii) Due to inflammation of bronchi and bronchioles.

Correct Answer: (a)
Asthma presents with breathing difficulty, wheezing, and airway inflammation. All three statements correctly describe the condition.

Q25. The chemosensitive area adjacent to the rhythm centre is highly sensitive to:

Correct Answer: (b)
The chemosensitive area in the medulla responds primarily to CO2 and hydrogen ion concentrations in the cerebrospinal fluid. Changes in these levels trigger adjustments in ventilation.

Q26. The site of actual diffusion of O2 and CO2 between blood and atmospheric air is the:

Correct Answer: (b)
The exchange part includes respiratory bronchioles, alveolar ducts, and alveoli. Here, the thin barrier between air and blood allows passive diffusion of oxygen into the blood and carbon dioxide out of it.

Q27. The 'Organ of Corti' is located on which membrane of the cochlea?

Correct Answer: (b)
The organ of Corti rests on the basilar membrane inside the cochlear duct. This membrane vibrates in response to sound, and the hair cells of the organ convert these vibrations into neural signals.

Q28. Which group of animals exchanges O2 and CO2 by simple diffusion over their entire body surface?

Correct Answer: (c)
Lower invertebrates like sponges and coelenterates lack specialized respiratory organs. Their body cells are in direct contact with water, allowing gases to diffuse across the entire body surface due to their thin, moist outer layers.

Q29. Which statements about 'Alveoli' are correct?
(i) Site of gas exchange.
(ii) Surrounded by network of capillaries.
(iii) Have thin squamous epithelium.

Correct Answer: (a)
Alveoli are the gas‑exchange sites, have a thin squamous epithelium, and are richly surrounded by capillaries. All statements are correct.

Q30. Which statements about 'Epiglottis' are correct?
(i) Thin elastic cartilaginous flap.
(ii) Prevents entry of food into larynx.
(iii) Covers glottis during swallowing.

Correct Answer: (a)
The epiglottis is a thin elastic flap that closes the glottis during swallowing, preventing food from entering the larynx. All statements are correct.

Q31. Identify correct matches for 'Volumes':
(i) TV = 500 mL.
(ii) RV = 1100-1200 mL.
(iii) VC = TV + IRV + ERV.

Correct Answer: (a)
TV ≈ 500 mL, RV ≈ 1100–1200 mL, and VC = TV + IRV + ERV. All three statements are correct.

Q32. Every 100 ml of deoxygenated blood delivers approximately ______ ml of CO2 to the alveoli.

Correct Answer: (a)
About 4 ml of CO2 is released from every 100 ml of deoxygenated blood as it passes through the pulmonary capillaries. This CO2 diffuses into the alveoli to be exhaled.

Q33. Assertion: Carbonic anhydrase is found in RBCs and plasma. Reason: It helps in the conversion of CO2 and water to bicarbonate.

Correct Answer: (d)
The reason is true: carbonic anhydrase catalyses CO2 hydration. However, the assertion is false because the enzyme is present mainly in RBCs, not in plasma. Thus assertion is false, reason is true.

Q34. Every 100 ml of oxygenated blood can deliver around ______ ml of O2 to the tissues.

Correct Answer: (b)
Under resting conditions, 100 ml of oxygenated blood releases about 5 ml of oxygen to the tissues. This is the difference between the oxygen content of arterial and venous blood.

Q35. Assertion: Occupational respiratory disorders cause serious lung damage. Reason: Long exposure to dust can lead to fibrosis (proliferation of fibrous tissues).

Correct Answer: (a)
Occupational lung diseases, such as silicosis, result from prolonged dust inhalation. Fibrosis is a hallmark of these disorders, causing scarring and reduced lung function, so the reason correctly explains the assertion.

Q36. Assertion: The role of oxygen in the regulation of respiratory rhythm is quite insignificant. Reason: Respiratory rhythm is mainly regulated by CO2 and H+ concentration.

Correct Answer: (a)
Under normal conditions, changes in CO2 and H+ are the primary drivers of respiratory rhythm; O2 levels have a minor influence. Thus the reason correctly supports the assertion.

Q37. Which of the following vertebrates uses gills for respiration?

Correct Answer: (c)
Among vertebrates, fishes are the primary group that use gills throughout their life. Gills are efficient for extracting dissolved oxygen from water, with counter-current flow mechanisms maximizing uptake.

Q38. Match the partial pressure in mm Hg (Blood Deoxygenated):

Gas	pO2/pCO2
A. O2	(I) 45
B. CO2	(II) 40

Correct Answer: (a)
In deoxygenated blood, pO2 is 40 mm Hg and pCO2 is 45 mm Hg, reflecting the partial pressures after gas exchange at the tissues.

Q39. Assertion: Every 100 ml of oxygenated blood can deliver around 5 ml of O2 to the tissues. Reason: Oxyhaemoglobin is formed in the alveoli and dissociates in the tissues.

Correct Answer: (a)
The assertion gives the typical O2 delivery volume. The reason explains the mechanism: oxyhaemoglobin formation in alveoli allows O2 pickup, and its dissociation in tissues releases O2, making the reason a valid explanation.

Q40. Identify the correct phylum/group being described:
(i) High pO2, low pCO2 in alveoli.
(ii) Low pO2, high pCO2 in tissues.
(iii) Diffusion occurs along concentration gradients.

Correct Answer: (a)
The statements describe the partial pressure differences that drive gas exchange between alveoli and tissues, which is the process of exchange of gases.

Q41. Which of the following is being described by the given statements?
(i) These are located in the thoracic chamber.
(ii) They are covered by a double layered pleura.
(iii) Their total volume can be Accommodation in the end of forced inspiration.

Correct Answer: (b)
The statements describe the lungs: they reside in the thorax, are covered by pleura, and their total capacity is measured at maximal inspiration. Alveoli are inside lungs, not the whole organ.

Q42. Assertion: The diffusion membrane is less than a millimetre thick. Reason: All factors in our body are favourable for diffusion of O2 from alveoli to tissues.

Correct Answer: (a)
The membrane is very thin, facilitating diffusion. The reason about 'all factors' is vague and does not explain why the membrane is thin; it merely states a general condition. Hence both are true but reason does not explain.

Q43. The solubility of CO2 is ______ times higher than that of O2.

Correct Answer: (c)
CO2 is about 20–25 times more soluble in blood plasma than oxygen. This high solubility aids in its efficient transport and rapid diffusion across respiratory membranes.

Q44. The lungs are situated in an air-tight chamber called the:

Correct Answer: (b)
The thoracic chamber (chest cavity) is bounded by ribs, sternum, and diaphragm. It is sealed from the abdominal cavity by the diaphragm, creating a closed space where pressure changes drive ventilation.

Q45. The partial pressure of oxygen (pO2) in the alveoli is ______ mm Hg.

Correct Answer: (b)
Alveolar pO2 is approximately 104 mm Hg. This is lower than atmospheric (159 mm Hg) because of mixing with residual air and the uptake of oxygen by pulmonary capillaries.

Q46. Additional volume of air a person can inspire by a forcible inspiration is:

Correct Answer: (b)
Inspiratory Reserve Volume (IRV) is the extra air that can be inhaled beyond a normal tidal breath. It represents the reserve capacity of the lungs and averages about 2500–3000 mL.

Q47. Match the organism in Column-I with its respiratory organ in Column-II:

Column-I (Organism)	Column-II (Organ)
A. Sponges	(I) Tracheal tubes
B. Earthworm	(II) Simple diffusion
C. Insects	(III) Gills
D. Fishes	(IV) Moist Cuticle

Correct Answer: (a)
Sponges rely on simple diffusion across their body surface; earthworms use their moist cuticle; insects have tracheal tubes for air transport; and fishes use gills for aquatic respiration.

Q48. Match the partial pressure in mm Hg (Blood Oxygenated):

Gas	pO2/pCO2
A. O2	(I) 40
B. CO2	(II) 95

Correct Answer: (a)
In oxygenated blood, pO2 is 95 mm Hg and pCO2 is 40 mm Hg, reflecting gas exchange in the pulmonary capillaries.

Q49. Regarding 'Oxygen Dissociation Curve', identify correct statements:
(i) It is sigmoid shaped.
(ii) Plot of % saturation of Hb with O2 vs pO2.
(iii) High H+ shift it to the right (dissociation).

Correct Answer: (a)
The curve is sigmoid, plotted as % saturation vs pO2; increased H+ and pCO2 shift it right, promoting O2 release. All are correct.

Q50. Assertion: Haemoglobin can carry a maximum of four molecules of O2. Reason: Haemoglobin is a red coloured iron containing pigment.

Correct Answer: (a)
The assertion is correct: each haemoglobin molecule binds up to four O2 molecules. The reason states a fact about its colour and iron content, but does not explain the binding capacity, which is due to its four polypeptide chains.

Q51. Match the gas transport amount:

Blood Type	Amount Delivered
A. 100ml Oxygenated blood	(I) 5ml O2
B. 100ml Deoxygenated blood	(II) 4ml CO2

Correct Answer: (a)
100 ml of oxygenated blood releases about 5 ml of O2 to tissues, while 100 ml of deoxygenated blood delivers about 4 ml of CO2 to the alveoli for exhalation.

Q52. Lungs are covered by a double-layered membrane called:

Correct Answer: (c)
The pleura is a serous membrane that envelops each lung. The visceral pleura adheres to the lung surface, while the parietal pleura lines the thoracic cavity; the pleural fluid between them reduces friction during breathing.

Q53. Assertion: The pneumotaxic centre is in the pons. Reason: It can reduce the duration of inspiration.

Correct Answer: (b)
Both statements are true: the pneumotaxic centre is located in the pons and does shorten inspiration. However, the location does not explain its function; they are separate facts.

Q54. Assertion: RBCs are nucleated in some organisms but not mammals. Reason: Mature human erythrocytes lack a nucleus.

Correct Answer: (a)
Both statements are true; however, the absence of a nucleus in humans is an example, not an explanation for why other organisms retain nuclei. Hence reason does not explain the assertion.

Q55. Occupational respiratory disorders like fibrosis are caused by long exposure to:

Correct Answer: (c)
Inhalation of fine dust particles (e.g., silica, asbestos) over many years leads to fibrosis – a thickening and scarring of lung tissue. This reduces lung elasticity and impairs gas exchange.

Q56. Assertion: Emphysema is a chronic disorder. Reason: One of the major causes is cigarette smoking.

Correct Answer: (a)
Emphysema is a long‑standing disease; smoking is a primary cause. The chronic nature arises from persistent damage, so the reason explains the assertion.

Q57. The cartilaginous box in the human respiratory system which helps in sound production is the:

Correct Answer: (c)
The larynx is a rigid box made of cartilage that houses the vocal cords. Air passing through causes the cords to vibrate, producing sound; its position and tension are adjusted for different pitches.

Q58. Assertion: Solubility of CO2 is 20-25 times higher than that of O2. Reason: The amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher.

Correct Answer: (a)
CO2 is indeed much more soluble than O2, and this high solubility directly increases its diffusion rate across the alveolar membrane. Therefore, the reason correctly explains the assertion.

Q59. Match the volumes in sequence of size (Smallest to Largest):

Rank	Volume
1st	TV (500)
2nd	ERV (1000-1100)
3rd	RV (1100-1200)
4th	IRV (2500-3000)

Correct Answer: (a)
The ascending order of lung volumes is: TV (500 mL) < ERV (1000–1100 mL) < RV (1100–1200 mL) < IRV (2500–3000 mL). This sequence is standard for healthy adults.

Q60. Match the capacity with its constituent volumes:

Column-I (Capacity)	Column-II (Volumes)
A. IC	(I) ERV + RV
B. EC	(II) TV + IRV
C. FRC	(III) ERV + TV + IRV
D. VC	(IV) TV + ERV

Correct Answer: (a)
Inspiratory Capacity (IC) = TV + IRV; Expiratory Capacity (EC) = TV + ERV; Functional Residual Capacity (FRC) = ERV + RV; Vital Capacity (VC) = ERV + TV + IRV.

Q61. Which part of the respiratory system humidifies and brings the air to body temperature?

Correct Answer: (b)
The conducting part (from nostrils to terminal bronchioles) conditions the incoming air by warming, moistening, and filtering it. This protects the delicate exchange surfaces from desiccation and particulate damage.

Q62. Match the partial pressure of O2 (pO2) with the site (Table 14.1):

Column-I (Site)	Column-II (pO2 in mm Hg)
A. Atmospheric Air	(I) 104
B. Alveoli	(II) 40
C. Oxygenated Blood	(III) 159
D. Tissues	(IV) 95

Correct Answer: (a)
Atmospheric pO2 is 159 mm Hg; alveolar pO2 is 104 mm Hg; oxygenated blood has 95 mm Hg; and tissues have 40 mm Hg. These gradients drive oxygen diffusion.

Q63. Match the scientists' focus:

Scientist	Discovery
A. Alfonso Corti	(I) Basilar membrane hair cells
B. Blackman	(II) Law of limiting factors (Unit Intro)

Correct Answer: (a)
Alfonso Corti discovered the organ of Corti and its hair cells on the basilar membrane; Blackman formulated the law of limiting factors in photosynthesis.

Q64. Which of the following is correct?
(i) RBCs carry 97% O2.
(ii) RBCs carry 20-25% CO2.
(iii) RBCs contain carbonic anhydrase.

Correct Answer: (a)
RBCs transport 97% of O2, 20–25% of CO2 (as carbamino‑haemoglobin), and contain carbonic anhydrase for bicarbonate formation. All statements are correct.

Q65. Assertion: CO2 diffuses from tissues to blood. Reason: pCO2 is higher in tissues (45 mm Hg) than in deoxygenated blood (40 mm Hg is incorrect; it's 45).

Correct Answer: (a)
The assertion is correct: CO2 moves from tissues to blood. However, the reason is false because pCO2 in deoxygenated blood is also 45 mm Hg, not 40; tissues and deoxygenated blood have equal pCO2, but the gradient is maintained by continuous removal of CO2 in the lungs.

Q66. Emphysema is a chronic disorder primarily caused by:

Correct Answer: (b)
Cigarette smoking is the leading cause of emphysema. It damages the alveolar walls, reducing the surface area for gas exchange and causing progressive breathlessness.

Q67. Total Lung Capacity (TLC) is the sum of:

Correct Answer: (a)
Total Lung Capacity is the total volume of air in the lungs after a maximal inspiration. It equals Vital Capacity plus Residual Volume (RV), as RV cannot be measured directly.

Q68. Match the disorder with its description:

Column-I (Disorder)	Column-II (Description)
A. Asthma	(I) Proliferation of fibrous tissues
B. Emphysema	(II) Inflammation of bronchi
C. Fibrosis	(III) Alveolar walls damaged

Correct Answer: (a)
Asthma involves inflammation of the airways; emphysema is characterized by destruction of alveolar walls; and fibrosis is the thickening and scarring of lung tissue.

Q69. Regarding 'Partial Pressure', which is true?
(i) pO2 in alveoli is 104 mm Hg.
(ii) pCO2 in alveoli is 40 mm Hg.
(iii) pO2 in oxygenated blood is 95 mm Hg.

Correct Answer: (a)
All listed partial pressures are correct: alveolar pO2 = 104, alveolar pCO2 = 40, and oxygenated blood pO2 = 95 mm Hg.

Q70. The trachea divides into right and left primary bronchi at the level of which vertebra?

Correct Answer: (b)
The trachea bifurcates at the level of the fifth thoracic vertebra (T5). This point, called the carina, marks the division into the two main bronchi that enter each lung.

Q71. Tidal Volume (TV) for a healthy man is approximately ______ mL per minute.

Correct Answer: (c)
TV per breath is about 500 mL; at a rate of 12–16 breaths/minute, the minute ventilation (TV × respiratory rate) is roughly 6000–8000 mL. This is the total volume of air moved in and out per minute.

Q72. The branching network of bronchi, bronchioles, and ______ comprise the lungs.

Correct Answer: (b)
Alveoli are the tiny air sacs at the terminal ends of bronchioles, where actual gas exchange occurs. Together with bronchi and bronchioles, they form the functional units of the lungs.

Q73. Earthworms use which structure for respiration?

Correct Answer: (c)
Earthworms respire through their moist skin (cuticle). The skin is richly supplied with blood capillaries, and oxygen dissolves in the moisture before diffusing into the blood, while carbon dioxide diffuses out.

Q74. Identify correct steps in 'Respiration':
(i) Breathing.
(ii) Diffusion across alveolar membrane.
(iii) Transport by blood.
(iv) Utilization of O2 by cells.

Correct Answer: (a)
Respiration includes ventilation (breathing), gas exchange at alveoli, blood transport, and cellular use of O2. All four steps are correct.

Q75. Match the partial pressure (Atmosphere):

Gas	mm Hg
A. O2	(I) 0.3
B. CO2	(II) 159

Correct Answer: (a)
In atmospheric air, partial pressure of O2 is 159 mm Hg and of CO2 is only 0.3 mm Hg, reflecting the composition of dry air.

Q76. Assertion: Inspiration is initiated by the contraction of diaphragm. Reason: Contraction of the diaphragm increases the volume of the thoracic chamber in the dorso-ventral axis.

Correct Answer: (c)
The assertion is true: diaphragm contraction triggers inspiration. However, the reason is false because diaphragm contraction increases the thoracic volume primarily in the vertical (superior-inferior) axis, not the dorso-ventral axis.

Q77. Assertion: A sigmoid curve is obtained when percentage saturation of haemoglobin with O2 is plotted against pO2. Reason: Sigmoid curve indicates that binding of the first O2 molecule facilitates the binding of others.

Correct Answer: (a)
The oxygen–haemoglobin dissociation curve is sigmoid due to cooperative binding: each O2 molecule bound makes it easier for subsequent ones to bind. This explains the curve's shape, so both are true and the reason is correct.

Q78. Match the breathing step with the event:

Step	Event
A. Inspiration	(I) Diaphragm relaxation
B. Expiration	(II) Diaphragm contraction

Correct Answer: (a)
Inspiration: diaphragm contracts and flattens; expiration: diaphragm relaxes and domes upward, reducing thoracic volume.

Q79. Match the transport mechanism with the percentage of gas:

Column-I (Gas & State)	Column-II (Percentage)
A. O2 by RBCs	(I) 70%
B. O2 in dissolved plasma	(II) 20-25%
C. CO2 as Bicarbonate	(III) 97%
D. CO2 by RBCs	(IV) 3%

Correct Answer: (a)
97% of O2 is carried by RBCs; 3% is dissolved in plasma. For CO2, 70% is transported as bicarbonate, 20–25% as carbamino-haemoglobin, and 7% dissolved in plasma.

Q80. The diffusion membrane is made up of how many major layers?

Correct Answer: (c)
The alveolar diffusion membrane consists of three layers: the thin squamous epithelium of the alveoli, the basement membrane, and the endothelium of the capillaries. Together they form a very thin barrier.

Q81. Vital Capacity (VC) is the sum of:

Correct Answer: (c)
Vital capacity is the maximum volume of air a person can expel after a maximal inspiration. It includes tidal volume (TV), inspiratory reserve volume (IRV), and expiratory reserve volume (ERV).

Q82. Which statement about 'Conducting Part' is correct?
(i) It consists of nostrils to terminal bronchioles.
(ii) It is the site of actual diffusion of O2 and CO2.
(iii) It clears air from foreign particles.

Correct Answer: (a)
The conducting part (nostrils to terminal bronchioles) filters, warms, and moistens air, but gas exchange occurs in the exchange part. Hence (i) and (iii) are correct.

Q83. Tracheal tubes as a respiratory mechanism are found in:

Correct Answer: (b)
Insects possess an elaborate network of tracheal tubes that branch throughout the body, delivering oxygen directly to tissues. Air enters through spiracles and travels via these tubes, bypassing the circulatory system for gas transport.

Q84. Match the vertebrate with its respiratory organ:

Vertebrate	Organ
A. Amphibians (Frog)	(I) Gills
B. Mammals	(II) Lungs and Skin
C. Fishes	(III) Lungs

Correct Answer: (a)
Frogs (amphibians) use lungs and skin for respiration; mammals have lungs; fishes use gills. These organs are adapted to their respective environments.

Q85. Identify the correct statements regarding 'Inspiration':
(i) Diaphragm contracts.
(ii) External intercostals contract.
(iii) Intra-pulmonary pressure becomes less than atmospheric pressure.

Correct Answer: (a)
Inspiration involves diaphragm contraction, external intercostal contraction (expanding the ribs), and a drop in intra‑pulmonary pressure below atmospheric. All three statements are correct.

Q86. Which muscles, along with the diaphragm, help in generation of pressure gradients for breathing?

Correct Answer: (c)
The intercostal muscles (external and internal) lie between the ribs. Their contraction or relaxation alters the volume of the thoracic cavity by moving the rib cage, contributing to the pressure changes needed for breathing.

Q87. On average, a healthy human breathes ______ times per minute.

Correct Answer: (b)
The normal respiratory rate at rest is 12–16 breaths per minute. This rate can vary with age, physical activity, and health status, but it generally remains within this range for healthy adults.

Q88. CO2 is carried by haemoglobin as:

Correct Answer: (b)
CO2 binds to the amino groups of haemoglobin to form carbamino-haemoglobin. This accounts for about 20–25% of CO2 transport; the rest is carried as bicarbonate or dissolved in plasma.

Q89. The pneumotaxic centre, which can moderate the functions of the rhythm centre, is in the:

Correct Answer: (b)
The pneumotaxic centre is located in the pons. It fine-tunes the respiratory rhythm by inhibiting the inspiratory centre, thus controlling the duration and rate of breathing.

Q90. Functional Residual Capacity (FRC) includes:

Correct Answer: (b)
Functional Residual Capacity is the volume of air remaining in the lungs after a normal expiration. It is the sum of Expiratory Reserve Volume (ERV) and Residual Volume (RV).

Q91. The process of exchange of O2 from the atmosphere with CO2 produced by the cells is called:

Correct Answer: (b)
Breathing is the physical process of taking in atmospheric oxygen and releasing carbon dioxide produced by cellular metabolism. It is the first step of respiration, involving ventilation and gas exchange.

Q92. Assertion: Vital Capacity is higher than Tidal Volume. Reason: Vital Capacity includes ERV, TV, and IRV.

Correct Answer: (a)
Vital capacity (sum of ERV, TV, IRV) is indeed greater than tidal volume alone. The reason correctly explains why VC > TV.

Q93. Assertion: Tidal volume is about 500 mL. Reason: It is the volume of air inspired or expired during a normal respiration.

Correct Answer: (a)
The definition of tidal volume (normal breath volume) directly gives its approximate value. Hence the reason correctly explains the assertion.

Q94. The respiratory rhythm centre is primarily located in the ______ region of the brain.

Correct Answer: (c)
The medulla oblongata houses the respiratory rhythm centre, which generates the basic pattern of breathing. It sends rhythmic impulses to the diaphragm and intercostal muscles.

Q95. Match the O2 delivery factors:

Factor	Effect on Hb Binding
A. High pO2	(I) Favour binding
B. High pCO2	(II) Favour dissociation
C. High H+	(III) Favour dissociation

Correct Answer: (a)
High pO2 promotes O2 binding to haemoglobin; high pCO2 and high H+ (acidic conditions) favour O2 dissociation, enhancing delivery to tissues.

Q96. Match the anatomy rule with the structure:

Column-I	Column-II
A. Sound box	(I) Pleura
B. Double layered membrane	(II) Larynx
C. Alveoli	(III) Alveolar ducts
D. Conducting part	(IV) Humidifies air

Correct Answer: (a)
Larynx is the sound box; lungs are covered by pleura (double membrane); alveoli are associated with alveolar ducts in the exchange part; and the conducting part warms and humidifies air.

Q97. Regarding 'Haemoglobin' binding:
(i) Favouring factors in alveoli: High pO2, low pCO2, low H+, lower temp.
(ii) Favouring dissociation in tissues: Low pO2, high pCO2, high H+, high temp.

Correct Answer: (a)
In the alveoli, conditions promote O2 binding; in tissues, conditions favour O2 release. Both sets of factors are correct.

Q98. The volume of air involved in breathing movements can be estimated using a:

Correct Answer: (b)
A spirometer is a device that measures the volume of air inhaled and exhaled. It provides various lung volumes and capacities, aiding in the diagnosis of pulmonary disorders.

Q99. Match the component of the diffusion membrane (Inside to Outside):

Layer	Name
A. Layer 1	(I) Squamous epithelium of alveoli
B. Layer 2	(II) Endothelium of alveolar capillaries
C. Layer 3	(III) Basement substance

Correct Answer: (a)
The diffusion membrane consists of the alveolar squamous epithelium, the capillary endothelium, and the basement membrane between them. The order from alveolar air to blood is epithelium → basement → endothelium.

Q100. Assertion: Diffusion of gases occurs in the alveolar region only. Reason: Alveoli and their ducts form the exchange part of the respiratory system.

Correct Answer: (a)
Gas exchange is confined to the exchange part (alveoli and ducts). The reason correctly identifies the anatomical region responsible, thus explaining the assertion.