Chapter 17 Breathing and Exchange of Gases
Multiple Choice Questions (MCQs)
1. Respiration in insects is called direct because
(a) the cells exchange $O_{2} / CO_{2}$ directly with the air in the tubes
(b) the tissues exchange $O_{2} / CO_{2}$ directly with coelomic fluid
(c) the tissues exchange $O_{2} / CO_{2}$ directly with the air outside through body surface
(d) tracheal tubes exchange $O_{2} / CO_{2}$ directly with the haemocoel which then exchange with tissues
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Answer
(a) Insects have a network of tubes (tracheal tubes) to transport atmospheric air within the body. These openings lead to trachae. The cells exchange $O_{2} / CO_{2}$ directly with the air in the spiracles present on insects body.
2. Which of the following does not occur during breathing?
(a) Brings the air to body temperature
(b) Warms up the air
(c) Diffusion of gases
(d) Cleans up the air
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Answer
(c) Diffusion of gases is a physical phenomenon that takes place between the tissue and blood vessels, and does not occur during breathing whereas bringing air to the body temperature, its cleaning and warming occurs during the process of breathing.
3. A person suffers punctures in his chest cavity in an accident, without any damage to the lungs its effect could be
(a) reduced breathing rate
(b) rapid increase in breathing rate
(c) no change in respiration
(d) cessation of breathing
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Answer
(d) The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. The pressure within the lungs is less than the atmospheric pressure so there is a negative pressure in the lungs with respect to atmospheric pressure.
The puncture in the chest affects this pressure gradient maintained by the lungs and thus may cause cessation of breathing.
4. It is known that exposure to carbon monoxide is harmful to animals because
(a) it reduces $CO_{2}$ transport
(b) it reduces $_{2}$ transport
(c) it increases $CO_{2}$ transport
(d) it increases $O_{2}$ transport
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Thinking Process
The reaction between haemoglobin and $\mathrm{CO}_{2}$ is reversible, whereas it is irreversible in case of $\mathrm{CO}$.
Answer
(b) Haemoglobin consist of a protein globin and pigment here. The four portion of iron in name combine with molecule of oxygen. It is an easy reversible reaction to form oxyhaemoglobin
$$ \mathrm{Hb}+O_{2} \rightleftharpoons HbO_{2} $$
Whereas, the complex formed by the reaction of carbon monooxide and haemoglobin is incredibly strong
$\underset{\text { (Haemoglobin) }}{\mathrm{Hb}+\mathrm{CO}} \rightarrow \underset{(\substack{\text { Carboxy } \\ \text { haemoglobin }})}{\mathrm{HbCO}}$
As a result of this strong between the haemoglobin and carbon monooxide the haemoglobin looses its affinity to oxygen thus may lead to choking or even death.
5. Mark the true statement among the following with reference to normal breathing
(a) inspiration is a passive process whereas expiration is active
(b) inspiration is a active process whereas expiration is passive
(c) inspiration and expiration are active processes
(d) inspiration and expiration are passive processes
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Answer
(b) Inspiration is a active process whereas expiration is a passive process. Inspiration occur when the muscles of diaphragm contrac to increase the overall volume of thoracic cavity.
Thus the pressure within the lungs (intra-pulmonary pressure) is less in comparison to the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure. As the muscles use energy for contraction inspiration is called active process.
Whereas, during the expiration diaphragm muscles relax without the use of energy intra-pulmonary pressure becomes higher than the atmospheric pressure and air noshes out. Thus, it is a passive process.
B. Expiration (chest cavity reduced)
6. A person breathes in some volume of air by forced inspiration after having a forced expiration. This quantity of air taken in is
(a) total lung capacity
(b) tidal volume
(c) vital capacity
(d) inspiratory capacity
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Answer
(c) The maximum volume of air that a person can breathe in after forced expiration or the maximum volume of air that a person can breathe out after forced inspiration is called vital capacity
$ \underset{\text { (Inspiratory reserve volume) }}{\mathrm{V} \mathrm{C}=\mathrm{I} \mathrm{R} \mathrm{V}} \underset{\text { (Expiratory reserve volume) }}{ + \mathrm{E} \mathrm{R} \mathrm{V}} + \underset{\text { (Tidal volume) }}{\mathrm{T} \mathrm{V}}$
The value of vital capacity varies from $3400 \mathrm{~mL}$ to $4800 \mathrm{~mL}$.
On the other hand, tidal volume is the air inspired or expired during normal breathing. Total lung capacity is the volume of air present in lungs and respiratory passage after maximum inspiration. Whereas, inspiratory capacity is total volume of air that a person can inspire after normal inspiration.
7. Mark the incorrect statement in context to $O_{2}$ binding to $\mathrm{Hb}$
(a) higher $\mathrm{pH}$
(b) lower temperature
(c) lower $p CO_{2}$
(d) higher $pO_{2}$
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Answer
(d) There are various factors which affect the binding of $\mathrm{O}_{2}$ with $\mathrm{Hb}$.
These factors are
(i) Low temperature
(ii) Low $\mathrm{H}^{+}$concentration (low pH).
(iii) Low diphosphoglyceraldehy
So, higher $\mathrm{pO}_{2}$ is the in correct statement.
8. Mark the correct pair of muscles involved in the normal breathing in humans.
(a) External and internal intercostal muscles
(b) Diaphragm and abdominal muscles
(c) Diaphragm and external intercostal muscles
(d) Diaphragm and intercostal muscles
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Answer
(d) The diaphragm and a specialised set of muscles, called external muscles present between the ribs are involved in the normal breathing in humans. They are involved in generating pressure gradient of air between the lungs and the atmosphere, so as to faeilitate the intake of air.
9. Incidence of emphysema a respiratory disorder is high in cigarette smokers. In such cases
(a) the bronchioles are found damaged
(b) the alveolar walls are found damaged
(c) the plasma membrane is found damaged
(d) the respiratory muscles are found damaged
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Answer
(b) Emphysema is a chronic disorder in which alveolar walls are damaged due to the infacation or obsomal distersion. It is a respiratory disorder caused by ciggrette smoking and inhalation of other smoke or toixic substences over a period of time.
10. Respiratory process is regulated by certain specialised centres in the brain. One of the following listed centres can reduce the inspiratory duration upon stimulation.
(a) Medullary inspiratory centre
(b) Pneumotaxic centre
(c) Apneustic centre
(d) Chemosensitive centre
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Answer
(b) Pneumotaxic Centre Located in the dorsal part of pons varoli of the brain can reduce the duration of inspiration and thus alter the respiratory rate.
Apneustic Centre Whereas is located in the lower part of pons varoli is responsible for promoting inspiration process.
Chemosensitive Centre is situated adjacent to the rhythm centre which is highly sensitive to $CO_{2}$ and hydrogen ions. Increase in $CO_{2}$ and $\mathrm{H}^{+}$in body and activates this centre for the elimiration of $\mathrm{CO}_{2}$ and $\mathrm{H}$
Medullary Inspiratory Centre is a specialised region present in medulla of the brain. and is primarily responsible for regulating the respiratory rhythm.
11. $ \mathrm{CO}_{2}$ dissociates from carbamino haemoglobin when
(a) $p CO_{2}$ is high and $p O_{2}$ is low
(b) $p O_{2}$ is high and $p CO_{2}$ is low
(c) $p CO_{2}$ and $p O_{2}$ are equal
(d) None of the above
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Thinking Process
$CO_{2}$ is carried by haemoglobin as carbamino haemoglobin. This binding is related to the partial pressure of $CO_{2}$.
Answer
(b) When, the $p CO_{2}$ is low and $pO_{2}$ is high as in the lung alveoli, dissociation of $CO_{2}$ from carbamino-haemoglobin takes place, $CO_{2}$ which is bound to haemoglobin from the tissue is delivered at the alveoli, to maintain the concentration of $CO_{2}$ thus increasing $pCO_{2}$.
Exchange of gases takes place between tissue capillary and tissue cells. Capillary cells with high $pO_{2}$ causes diffusion of $O_{2}$ into tissue cells via tissue fluid on the other hand high $p CO_{2}$ in the tissue cells causes diffusion of $CO_{2}$ into tissue capillary via tissue fluid.
12. In breathing movements, air volume can be estimated by (a) stethoscope (b) hygrometer (c) sphygmomanometer (d) spirometer
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Answer
(d) Spirometer is the device used to measure the volume of air involved in breathing movements and it also helps in clinical assessment of pulmonary functions.
Stethoscope is a medical device used for listening the internal sounds of an animal or human body.
Hygrometer is a device used for measuring the moisture content in the atmosphere, i.e., humidity.
Sphygmomanometer is a device that is used to measure blood pressure.
13. From the following relationships between respiratory volume and capacities, mark the correct option.
(i) Inspiratory Capacity (IC) =Tidal Volume +Residual Volume
(ii) Vital Capacity (VC) = Tidal Volume (TV) + Inspiratory Reserve Volume (IRV) + Expiratory Reserve Volume (ERV).
(iii) Residual Volume (RV) = Vital Capacity (VC) - Inspiratory Reserve Volume (IRV)
(iv) Tidal Volume (TV) = Inspiratory Capacity (IC) - Inspiratory Reserve Volume (IRV)
Options
(a) (i) Incorrect, (ii) Incorrect, (iii) Incorrect, (iv) Correct
(b) (i) Incorrect, (ii) Correct, (iii) Incorrect, (iv) Correct
(c) (i) Correct, (ii) Correct, (iii) Incorrect, (iv) Correct
(d) (i) Correct, (ii) Incorrect, (iii) Correct, (iv) Incorrect
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Answer
(b) (i) Inspiratory Capacity (IC) =Tidal Volume + Inspiratory Reserve Volume (TV + IRV).
(ii) Vital Capacity (VC) Tidal Volume + Inspiratory Reserve Volume + Expiratory Reserve Volume. (TV + ERV + IRV)
(iii) Residual Volume (RV) Volume of air remaining in the lungs after a forcible expiration.
(iv) Tidal Volume (TV) Volume of air inspired or expired during a normal respiration.
14. The oxygen-haemoglobin dissociation curve will show a right shift in case of
(a) high $p \mathrm{CO}_{2}$
(b) high $\mathrm{pO}_{2}$
(c) low $p \mathrm{CO}_{2}$
(d) less $\mathrm{H}^{+}$concentration
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Answer
(a) A sigmoid curve obtained when percentage saturation of haemogblobin with $O_{2}$ is plotted against the $pO_{2}$.
The oxygen haemoglobin dissociation curve is shifted to right under following condition.
(i) Decrease in partial pressure of oxygen.
(ii) Increase in partial pressure of carbonoxide.
(iii) Increase in hydrogen concentration.
(iv) Decrease in $\mathrm{pH}$ activity.
(v) Increased body temperature.
15. Match the following columns.
| Column I | Coulmn II | ||
|---|---|---|---|
| A. | Earthworm | 1. | Moist cuticle |
| B. | Aquatic arthropods | 2. | Gills |
| C. | Fishes | 3. | Lungs |
| D. | Birds/Reptiles | 4. | Trachea |
Options
| A | B | C | D | |
|---|---|---|---|---|
| (a) | 2 | 1 | 4 | 3 |
| (b) | 1 | 4 | 2 | 3 |
| (c) | 1 | 3 | 2 | 4 |
| (d) | 1 | 2 | 4 | 3 |
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Answer
(b) Earthworm respire through their moist cuticle and aquatic arthropods, respire through trachea.
Fishes respire through gills, and birds/reptiles respire through lungs.
Very Short Answer Type Questions
1. Define the following terms?
(a) Tidal volume
(b) Residual volume
(c) Asthma
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Thinking Process
The quantity of air that lung can receive, hold or expel under different condition is called pulmonary volume. Combination of two or more pulmonary volume is called pulmonary capacities.
Answer
(a) Tidal Volume (TV) is the volume of air inspired or expired during normal breath. This is about $500 \mathrm{~mL}$, i.e., a healthy man inspire or expire about 6000 to $8000 \mathrm{~mL}$ of air per minute.
(b) Residual Volume (RV) is the volume of air remaining in the lungs even after a forcible expiration. It is about $1100 \mathrm{~mL}$ to $1200 \mathrm{~mL}$.
(c) Asthma It is a disease caused due to an allergic reaction to foreign substances. The major symptoms are difficulty in breathing causing wheezing and coughing. Due to the inflammation of bronchi.
2. A fluid filled double membranous layer surrounds the lungs. Name it and mention its important function.
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Answer
A fluid filled double membranous layer that surrounds the lungs is called pleura, and fluid is pleural fluid in between them. The outer pleural membrane is in close contact with the thoracic lining whereas, the inner pleural membrane is in contact with the lung surface. These collectively reduce friction on lung’s surface.
3. Name the primary site of exchange of gases in our body?
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Answer
The primary site for the exchange of gases in our body is alveoli. There are 300 millions of alveoli collectively in both the lungs. These alveoli have very thin wall consisting of squamous epithelium. With extensive network of blood capillaries.
The presence of blood capillaries in the alveoli, result in easy exchange of gases. Each alveolus is also called as miniature lung.
4. Cigarette smoking causes emphysema. Give reason.
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Answer
Emphysema is a chronic disorder of respiratory system, where inflation or abnormal distension of alveolar wall occurs. Cigarette smoking and the inhalation of other smoke or toxic substances over a period of time causes the damaging of septa between the alveoli, and of its elastic tissue is replaced by the connective tissue in lungs.
Hence, the respiratory surface decreases, thus causing the emphysema. It causes shortness of breath, production of sputum, chronic bronchitis, etc.
5. What is the amount of $O_{2}$ supplied to tissues through every $100 \mathrm{~mL}$ of oxygenated blood under normal physiological conditions?
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Answer
Every $100 \mathrm{~mL}$ of oxygenated blood can deliver around $5 \mathrm{~mL}$ of $\mathrm{O}_{2}$ to the tissue under normal physiological conditions.
6. A major percentage ( $97 \%$ ) of $O_{2}$ is transported by RBCs in the blood. How does the remaining percentage ( $3 \%$ ) of $O_{2}$ transported?
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Answer
About $97 \%$ of $O_{2}$ is transported by RBCs in the blood. The remaining $3 \%$ of $O_{2}$ is carried in a dissolved state through the plasma.
7. Arrange the following terms based on their volumes in an ascending order.
(a) Tidal Volume (TV)
(b) Residual Volume (RV)
(c) Inspiratory Reserve Volume (IRV)
(d) Expiratory Capacity (EC)
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Answer
(d) Expiratory Capacity (EC) Approximate volume is $1000 \mathrm{~mL}$.
(b) Residual Volume (RV) Approximate volume is $1200 \mathrm{~mL}$.
(c) Inspiratory Reserve Volume (IRV) Approximate volume is 2500 to $3000 \mathrm{~mL}$.
(a) Tidal Volume(TV) Approximate volume is 6000 to $8000 \mathrm{~mL}$.
8. Complete the missing terms
(a) Inspiratory Capacity (IC) $=\ldots+$ IRV
(b) $\ldots=\mathrm{TV}+\mathrm{ERV}$
(c) Functional Residual Capacity (FRC) $=$ ERV $+\ldots$
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Answer
(a) Inspiratory Capacity (IC) $=(\mathrm{TV})+(\mathrm{IRV})$ Tidal Volume. Inspiratory Reserve Volume
(b) Expiratory Capacity $(E C)=(T V+E R V)$ Tidal Volume. Expiratory Reserve Volume
(c) Functional Residual Capacity (FRC) $=($ ERV ) Expiratory $+($ RV $)$ Reserve Volume. Residual Volume
9. Name the organs of respiration in the following organisms.
(a) Flatworm
(b) Birds
(c) Frog
(d) Cockroach
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Thinking Process
Mechanism of breathing vary among different groups of animals depending on their habitats and levels of organisation.
Answer
(a) Flatworm General body surface
(b) Birds Lungs
(c) Frog Lungs and moist skin
(d) Cockroach Tracheal tubes
10. Name the important parts involved in creating a pressure gradient between lungs and the atmosphere during normal respiration.
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Answer
The diaphragm and a specialised set of external and intercostals muscles between the ribs, help in the generation of pressure gradient during normal respiration.
Short Answer Type Questions
1. State the different modes of $CO_{2}$ transport in blood.
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Answer
Carbon dioxide is carried by the blood in three forms
(i) In Dissolved State Under normal temperature and pressure, about $7 \%$ of $\mathrm{CO}_{2}$ is carried by physical solution.
(ii) As Carbamino Compounds
$CO_{2}$ binds directly with $Hb$ to form an unstable compound carbaminocompounds $(CO_{2} )$ About $23 \%$ $CO_{2}$ is transported in this form. When $p CO_{2}$ is high and $pO_{2}$ is low as in the tissues, more binding of carbon-dioxide occurs whereas, when $p CO_{2}$ is low and $pO_{2}$ is high as in alveol as tissue dissociation of $CO_{2}$ from carbamino-haemoglobin takes place.
$$ HbO_{2}+CO_{2} \rightleftharpoons HbCO_{2}+\mathrm{H}^{+}+O_{2} $$
(iii) As Bicarbonate lons $CO_{2}$ reacts with water to form carbonic acid $\left(H_{2} CO_{3}\right)$ in the presence of carbonic anhydrase in RBC. $H_{2} CO_{3}$ dissociates into hydrogen and bicarbonate ions $\left(HCO_{3}{ }^{-}\right)$.
The whole reaction proceeds as follows
$\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \underset{\text { Anhydrase }}{\stackrel{\text { Carbonic }}{\rightleftarrows}} \underset{\text { Carbonic acid }}{\mathrm{H}_2 \mathrm{CO}_3}$
$\underset{\text { Carbonic acid }}{\mathrm{H}_2 \mathrm{CO}_3} \rightleftharpoons \underset{\substack{\text { Hydrogen } \\ \text { ion }}}{\mathrm{H}^{+}}+\underset{\substack{\text { Bicarbonate } \\ \text { ion }}}{\mathrm{HCO}_3^{-}}$
The carbonic anhydrase reaction mainly occur in RBC as it contain high concentration of enzyme carbonic anhydrase and minute quantity of it is present in plasma too.
2. Compared to $O_{2}$, diffusion rate of $CO_{2}$ through the diffusion membrane per unit difference in partial pressure is much higher. Explain.
Show Answer
Thinking Process
Diffusing capacity can be defined as the volume of gas, that diffuses through the membrane per minute for a pressure difference of $1 \mathrm{~mm} \mathrm{Hg}$. It is further dependent on the solubility of the diffusing gases.
Answer
As, the solubility rate of $CO_{2}$ is $20-25$ times higher than that of the $O_{2}$, the amount of $CO_{2}$ that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of $O_{2}$.
3. For completion of respiration process, write the given steps in sequential manner.
(a) Diffusion of gases $\left(O_{2}\right.$ and $\left.CO_{2}\right)$ across alveolar membrane.
(b) Transport of gases by blood.
(c) Utilisation of $O_{2}$ by the cells for catabolic reactions and resultant release of $CO_{2}$.
(d) Pulmonary ventilation by which atmospheric air is drawn in and $\mathrm{CO}_{2}$ rich alveolar air is released out.
(e) Diffusion of $O_{2}$ and $CO_{2}$ between blood and tissues.
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Answer
(d) Pulmonary ventilation by which atmospheric air is drawn in and $CO_{2}$ rich alveolar air is released out.
(a) Diffusion of gases $\left(O_{2}\right.$ and $\left.CO_{2}\right)$ across alveolar membrane.
(b) Transport of gases by blood.
(c) Diffusion of $O_{2}$ and $CO_{2}$ between blood and tissues.
(e) Utilisation of $O_{2}$ by the cells for catabolic reactions and resultant release of $CO_{2}$.
4. Differentiate between
(a) Inspiratory and expiratory reserve volume
(b) Vital capacity and total lung capacity.
(c) Emphysema and occupational respiratory disorder.
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Answer
Difference between these are as follows
(a)
| Inspiratory Reserve Volume | Expiratory Reserve Volume |
|---|---|
| It is the additional volume of air, a person can inspire by a forcible inspiration. It ranges between $2500 \mathrm{~mL}$ to $3000 \mathrm{~mL}$. |
(b)
| Vital Capacity | Total Lung Capacity |
|---|---|
| Vital capacity is the maximum volume of air that a person can breathe in after a forced expiration. This includes ERV, TV and IRV or the maximum volume of air a person can breathe out after a forced inspiration. i.e., Vc = ERV + IRV + TV | Total using capacity is the total volume of air accommodated in the lungs at the end of a forced inspiration. This includes RV, ERV, TV and IRV or vital capacity + residual volume. i.e., TLC = RV + ( ERV + IRV +TV) or VC + RV |
(c)
| Emphysema | Occupational Respiratory Disorder |
|---|---|
| Emphysema is a chronic disorder of respiratory system, in which alveolar damaged due to which regulatory respiratory surface is decreased. | It is caused due to the long exposure of dust produced by stone grinding or breaking and give rise to inflammation leading to fibrosis and thus causing serious lung damage. Protective masks are provided for the |
| Cause of emphysema is cigarette smoking. |
Long Answer Type Questions
1. Explain the transport of $O_{2}$ and $CO_{2}$ between alveoli and tissue with diagram.
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Answer
Representing the transport of $O_{2}$ and $CO_{2}$ between alveoli and tisue with diagram
2. Explain the mechanism of breathing with neat labelled sketches.
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Answer
Mechanism of Breathing Breathing involves two stages, inspiration during which atmospheric air is drawn in and expiration by which the alveolar air is released out.
The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere, the help of diaphragm and inter costal muscles.
3. Explain the role of neural system in regulation of respiration.
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Answer
Human beings have a significant ability to maintain and moderate the respiratory rhythm to suit the demands of the body tissue. This is done by the neural system.
Respiration regulated by neural system in following ways/ manress
(i) A specialised centre present in the medulla region of the brain called respiratory rhythm centre is primarily responsible in regulating respiration process. Another centre present in the pons region of the brain called pneumotaxic centre, can moderate the functions of the respiratory rhythm centre. Neural signal from this centre, can reduce the duration of inspiration and thereby alter the respiratory rate.
(ii) A chemosensitive area is situated adjacent to the rhythm centre which is highly sensitive to $\mathrm{CO}_{2}$ and hydrogen ions. Increase in these substances activates this centre, which in turn signals the rhythm centre to make necessary adjustments in the respiratory process by which these substances can be eliminated.
(iii) Receptors associated with aortic arch and carotid artery also recognise changes in $\mathrm{CO}_{2}$ and $\mathrm{H}^{+}$concentration and send necessary signals to the rhythm centre for remedial action because the role of oxygen in the regulation of respiratory rhythm is quite insignificant.
