Chapter 14: Breathing and Exchange of Gases Long Questions | biology Class 11 CBSE

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Chapter 14: Breathing and Exchange of Gases Long Questions | biology Class 11 CBSE | ByteNotes.in

Long Answer

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Question 1

Long Form

Trace the pathway of air from the external nostrils to the alveoli, naming all structural components and highlighting the role of cartilaginous support.

Air enters through external nostrils, passes through the nasal passage into the nasal chamber, then into the pharynx — a common passage for both food and air.
From the pharynx, air passes through the larynx (the cartilaginous sound box, where the epiglottis covers the glottis during swallowing) into the trachea, a straight cartilage-supported tube extending to mid-thorax.
The trachea divides at the 5th thoracic vertebra into the right and left primary bronchi, which undergo repeated divisions to form secondary and tertiary bronchi, and then bronchioles.
The trachea, primary, secondary, tertiary bronchi, and initial bronchioles are all supported by incomplete cartilaginous rings that prevent their collapse during breathing.
The bronchioles end in very thin terminal bronchioles, which give rise to alveoli — thin, irregular-walled, vascularised bag-like structures that are the site of gas exchange.
The branching network of bronchi, bronchioles, and alveoli together comprise the two lungs, which are enclosed in a double-layered pleura with friction-reducing pleural fluid between the layers.

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Question 2

Long Form

Describe the mechanism of normal inspiration and expiration, explaining how pressure gradients are created and resolved.

Breathing involves two stages: inspiration (air drawn in) and expiration (alveolar air expelled), both carried out by creating pressure gradients between lungs and atmosphere.
During inspiration, the diaphragm contracts and flattens, increasing thoracic volume in the antero-posterior axis; simultaneously, external intercostal muscles contract, lifting the ribs and sternum to increase thoracic volume in the dorso-ventral axis.
The overall increase in thoracic volume causes a corresponding increase in pulmonary volume, which decreases intra-pulmonary pressure to below atmospheric pressure, forcing air from outside into the lungs.
During expiration, relaxation of the diaphragm and intercostal muscles returns them to their normal positions, reducing thoracic and pulmonary volume.
This reduction raises intra-pulmonary pressure slightly above atmospheric pressure, causing the expulsion of alveolar air from the lungs.
Additional abdominal muscles can augment both inspiration and expiration when stronger effort is needed; normal breathing rate is 12–16 times per minute in a healthy adult, and a spirometer is used to measure air volumes clinically.

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Question 3

Long Form

Compare and analyse all respiratory volumes and capacities in the human body, providing values and formulas where applicable.

The four basic respiratory volumes are: Tidal Volume (TV) ≈ 500 mL (normal breath); Inspiratory Reserve Volume (IRV) = 2500–3000 mL (extra volume on forcible inspiration); Expiratory Reserve Volume (ERV) = 1000–1100 mL (extra volume on forcible expiration); Residual Volume (RV) = 1100–1200 mL (air remaining even after forcible expiration).
Inspiratory Capacity (IC) = TV + IRV — the total air inspirable after normal expiration.
Expiratory Capacity (EC) = TV + ERV — the total air expirable after normal inspiration.
Functional Residual Capacity (FRC) = ERV + RV — air remaining after normal expiration, maintaining alveolar patency between breaths.
Vital Capacity (VC) = ERV + TV + IRV — the maximum air exchangeable; reflects overall lung function and is clinically significant.
Total Lung Capacity (TLC) = VC + RV = RV + ERV + TV + IRV — the maximum air the lungs can hold; all these capacities are measured by a spirometer and used for clinical diagnosis of pulmonary disorders.

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Question 4

Long Form

Analyse the factors that determine the direction and rate of diffusion of O2 and CO2 across alveolar and tissue membranes, using the partial pressure data from the chapter.

Gases diffuse from regions of higher partial pressure to lower partial pressure; the rate of diffusion also depends on solubility of the gas and thickness of the diffusion membrane.
pO2 in atmospheric air is 159 mm Hg; in alveoli 104 mm Hg; in deoxygenated blood 40 mm Hg; in oxygenated blood 95 mm Hg; and in tissues 40 mm Hg — establishing a gradient that drives O2 from alveoli → blood → tissues.
pCO2 in tissues is 45 mm Hg; in deoxygenated blood 45 mm Hg; in alveoli 40 mm Hg — establishing a gradient that drives CO2 from tissues → blood → alveoli, opposite to O2.
CO2 has a solubility 20–25 times higher than O2, so despite a smaller partial pressure gradient, CO2 diffuses efficiently across the membrane.
The diffusion membrane is extremely thin (much less than 1 mm), comprising squamous alveolar epithelium, basement substance, and endothelium of capillaries — its minimal thickness greatly facilitates diffusion.
Thus, all body conditions — partial pressure gradients, high CO2 solubility, and ultra-thin diffusion membrane — are simultaneously favourable for O2 to move from alveoli to tissues and CO2 to move in the reverse direction.

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Question 5

Long Form

Describe the transport of oxygen in blood, explaining the factors that influence haemoglobin's affinity for oxygen with reference to the oxygen dissociation curve.

About 97% of O2 is transported as oxyhaemoglobin — haemoglobin binds O2 reversibly, with each molecule capable of carrying up to four O2 molecules; the remaining 3% is dissolved in plasma.
Binding of O2 to haemoglobin is primarily determined by pO2; additionally, pCO2, H+ concentration, and temperature also influence it.
The oxygen dissociation curve is a sigmoid (S-shaped) curve obtained when % saturation of haemoglobin with O2 is plotted against pO2; its shape reflects cooperative binding among haemoglobin's four subunits.
In the alveoli — high pO2 (104 mm Hg), low pCO2, low H+, lower temperature — conditions favour O2 loading onto haemoglobin (oxyhaemoglobin formation).
In tissues — low pO2 (40 mm Hg), high pCO2, high H+ concentration (Bohr effect), higher temperature — conditions favour dissociation of O2 from oxyhaemoglobin (O2 unloading to cells).
Every 100 mL of oxygenated blood delivers approximately 5 mL of O2 to the tissues under normal physiological conditions, demonstrating the efficiency of haemoglobin-based transport.

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Question 6

Long Form

Describe the three mechanisms by which CO2 is transported from tissues to the alveoli, highlighting the role of carbonic anhydrase.

CO2 is transported by blood in three ways: (i) as bicarbonate ions (HCO3–) — approximately 70%; (ii) as carbamino-haemoglobin bound to haemoglobin — 20–25%; and (iii) dissolved in plasma — about 7%.
The enzyme carbonic anhydrase, present in very high concentration in RBCs (and in minute quantity in plasma), catalyses a reversible reaction: CO2 + H2O ⇌ H2CO3 ⇌ HCO3– + H+.
At the tissue site, high pCO2 drives CO2 into blood; carbonic anhydrase catalyses the forward reaction, forming HCO3– and H+ — CO2 is thus trapped as bicarbonate for transport.
At the alveolar site, low pCO2 drives the reaction in reverse — bicarbonate recombines with H+ to form CO2 and H2O, and CO2 is expelled in expired air.
For carbamino-haemoglobin transport, when pCO2 is high and pO2 is low (tissues), CO2 binds more to haemoglobin; when pCO2 is low and pO2 is high (alveoli), CO2 dissociates from carbamino-haemoglobin.
Every 100 mL of deoxygenated blood delivers approximately 4 mL of CO2 to the alveoli, demonstrating the quantitative effectiveness of these combined mechanisms.

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Hard

Question 7

Long Form

Explain the neural regulation of respiration, describing the roles of different brain centres and chemoreceptors.

The human nervous system regulates respiratory rhythm to suit the metabolic demands of body tissues; this involves multiple brain centres and peripheral receptors.
The respiratory rhythm centre in the medulla oblongata is primarily responsible for generating and maintaining the basic rhythm of breathing.
The pneumotaxic centre in the pons region of the brain can moderate the rhythm centre: neural signals from the pneumotaxic centre reduce the duration of inspiration, thereby increasing respiratory rate.
A chemosensitive area adjacent to the rhythm centre in the medulla is highly sensitive to elevated CO2 and H+ ion concentrations; when these rise, it activates the rhythm centre to increase breathing rate and eliminate the excess.
Peripheral receptors in the aortic arch and carotid artery also detect changes in CO2 and H+ concentration and relay signals to the rhythm centre for remedial adjustments.
Notably, the role of O2 in regulating respiratory rhythm is described as quite insignificant — the system is primarily CO2/H+-driven, emphasising how CO2 accumulation is the principal stimulus for increased ventilation.

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Question 8

Long Form

Compare and contrast the respiratory mechanisms in lower invertebrates, earthworms, insects, aquatic arthropods, and mammals.

Respiratory mechanisms vary according to habitat and level of organisation; lower invertebrates (sponges, coelenterates, flatworms) exchange O2 and CO2 by simple diffusion over their entire body surface — the simplest mechanism.
Earthworms use their moist cuticle for cutaneous respiration — diffusion across the moist skin surface is sufficient given their small body size and metabolic demand.
Insects have a network of tracheal tubes that transport atmospheric air directly within the body, bypassing blood as the transport medium for respiratory gases.
Aquatic arthropods and molluscs use special vascularised structures called gills (branchial respiration) to exchange gases with dissolved oxygen in water.
Terrestrial vertebrates including mammals use vascularised lungs (pulmonary respiration), where gas exchange occurs at alveoli; amphibians like frogs also supplement pulmonary breathing with cutaneous respiration through their moist skin.
Among vertebrates, fishes use gills; amphibians, reptiles, birds, and mammals use lungs — this progression reflects increasing metabolic demands and adaptation to terrestrial life, requiring more efficient, dedicated respiratory structures.

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Long Answer

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Question 9

Long Form

Analyse the five steps of respiration as described in the chapter, explaining how they are sequentially interconnected.

Step 1 — Pulmonary ventilation (breathing): atmospheric air is drawn into the lungs during inspiration, and CO2-rich alveolar air is released during expiration, driven by pressure gradients created by the diaphragm and intercostal muscles.
Step 2 — Diffusion of gases across alveolar membranes: O2 from alveolar air diffuses into deoxygenated blood (down its pressure gradient); CO2 from blood diffuses into alveolar air (down its gradient), facilitated by the thin diffusion membrane.
Step 3 — Transport of gases by blood: O2 is carried as oxyhaemoglobin (97%) and dissolved (3%); CO2 is carried as bicarbonate (70%), carbamino-haemoglobin (20–25%), and dissolved (7%).
Step 4 — Diffusion of O2 and CO2 between blood and tissues: at the tissue level, O2 moves from oxygenated blood (pO2 = 95 mm Hg) to tissues (pO2 = 40 mm Hg); CO2 moves from tissues (pCO2 = 45 mm Hg) into blood.
Step 5 — Cellular respiration: O2 is utilised by cells for catabolic reactions — oxidative breakdown of glucose, amino acids, and fatty acids — to produce energy (ATP), with CO2 as a by-product.
These steps form a continuous, linked cycle: cellular metabolism creates the CO2/O2 gradient that drives diffusion, which drives transport, which drives ventilation — the entire process is regulated by CO2-sensitive neural centres.

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Question 10

Long Form

Describe the disorders of the respiratory system covered in the chapter, analysing their causes, mechanisms, and consequences.

Three respiratory disorders are described: Asthma, Emphysema, and Occupational Respiratory Disorders — each affecting different levels of the respiratory system.
Asthma is a difficulty in breathing causing wheezing; its mechanism involves inflammation of bronchi and bronchioles, which narrows the airways and restricts airflow — primarily affecting the conducting part.
Emphysema is a chronic disorder characterised by damage to alveolar walls; destruction of alveoli decreases the respiratory surface available for gas exchange, severely impairing O2 uptake and CO2 release.
Cigarette smoking is identified as one of the major causes of emphysema, demonstrating a direct link between lifestyle and progressive lung destruction.
Occupational respiratory disorders arise in industries involving grinding or stone-breaking; excessive dust production overwhelms the body's natural defence mechanisms.
Long-term dust exposure in such occupations leads to inflammation and then fibrosis — proliferation of fibrous tissue in the lungs — causing serious and potentially irreversible lung damage; protective masks are the recommended preventive measure.

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Chapter 14: Breathing and Exchange of Gases | Long Questions

Trace the pathway of air from the external nostrils to the alveoli, naming all structural components and highlighting the role of cartilaginous support.

Describe the mechanism of normal inspiration and expiration, explaining how pressure gradients are created and resolved.

Compare and analyse all respiratory volumes and capacities in the human body, providing values and formulas where applicable.

Analyse the factors that determine the direction and rate of diffusion of O2 and CO2 across alveolar and tissue membranes, using the partial pressure data from the chapter.

Describe the transport of oxygen in blood, explaining the factors that influence haemoglobin's affinity for oxygen with reference to the oxygen dissociation curve.

Describe the three mechanisms by which CO2 is transported from tissues to the alveoli, highlighting the role of carbonic anhydrase.

Explain the neural regulation of respiration, describing the roles of different brain centres and chemoreceptors.

Compare and contrast the respiratory mechanisms in lower invertebrates, earthworms, insects, aquatic arthropods, and mammals.

Analyse the five steps of respiration as described in the chapter, explaining how they are sequentially interconnected.

Describe the disorders of the respiratory system covered in the chapter, analysing their causes, mechanisms, and consequences.

Unlock all Long Questions