NCERT solutions- Breathing & Exchange of gases Notes - Class 11

Class 11: NCERT solutions- Breathing & Exchange of gases Notes - Class 11

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 Page 1


Breathing And Exchange of Gases 
Question 1. Define vital capacity. What is its significance? 
Answer: Vital Capacity (VC): The maximum volume of air a person can breathe in 
after a forced expiration. This includes ERV (Expiratory Reserve Volume), TV (Tidal 
Volume) and IRV (Inspiratory Reserve Volume) or the maximum volume of air a 
person can breathe out after a forced inspiration. 
Question 2. State the volume of air remaining in the lungs after a normal 
breathing. 
Answer: Functional Residual Capacity (FRC): Volume of air that will remain in the 
lungs after a normal expiration. This includes ERV+RV. 
ERV=1000 to 1100 ml 
RV = 1100 to 1200 ml 
So, FRC = 2100 to 2300 ml 
Question 3. Diffusion of gases occurs in the alveolar region only and not in the 
other parts of respiratory system. Why? 
Answer:- EXCHANGE OF GASES 
Alveoli are the primary sites of exchange of gases. Exchange of gases also occur 
between blood and tissues. O
2
 and CO
2
 are exchanged in these sites by simple 
diffusion mainly based on pressure/concentration gradient. 
Alveolar region is having enough pressure gradient to facilitate diffusion of gases. 
Other regions of the respiratory system don’t have the required pressure gradient. 
Solubility of the gases as well as the thickness of the membranes involved in 
diffusion are also some of the important factors that can affect the rate of diffusion. 
Pressure contributed by an individual gas in a mixture of gases is called partial 
pressure and is represented as pO
2
 for oxygen and pCO
2
 for carbon dioxide. 
Question 4. What are the major transport mechanisms for CO
2
? Explain. 
Answer:- Transport of Carbon dioxide 
CO
2
 is carried by haemoglobin as carbamino-haemoglobin (about 20-25 per cent). 
This binding is related to the partial pressure of CO
2
. 
pO
2
 is a major factor which could affect this binding. When pCO
2
 is high and pO
2
 is 
low as in the tissues, more binding of carbon dioxide occurs whereas, when the 
pCO
2
 is low and pO
2
 is high as in the alveoli, dissociation of CO
2
 from carbamino-
haemoglobin takes place, i.e., CO
2
 which is bound to haemoglobin from the tissues 
is delivered at the alveoli. 
Page 2


Breathing And Exchange of Gases 
Question 1. Define vital capacity. What is its significance? 
Answer: Vital Capacity (VC): The maximum volume of air a person can breathe in 
after a forced expiration. This includes ERV (Expiratory Reserve Volume), TV (Tidal 
Volume) and IRV (Inspiratory Reserve Volume) or the maximum volume of air a 
person can breathe out after a forced inspiration. 
Question 2. State the volume of air remaining in the lungs after a normal 
breathing. 
Answer: Functional Residual Capacity (FRC): Volume of air that will remain in the 
lungs after a normal expiration. This includes ERV+RV. 
ERV=1000 to 1100 ml 
RV = 1100 to 1200 ml 
So, FRC = 2100 to 2300 ml 
Question 3. Diffusion of gases occurs in the alveolar region only and not in the 
other parts of respiratory system. Why? 
Answer:- EXCHANGE OF GASES 
Alveoli are the primary sites of exchange of gases. Exchange of gases also occur 
between blood and tissues. O
2
 and CO
2
 are exchanged in these sites by simple 
diffusion mainly based on pressure/concentration gradient. 
Alveolar region is having enough pressure gradient to facilitate diffusion of gases. 
Other regions of the respiratory system don’t have the required pressure gradient. 
Solubility of the gases as well as the thickness of the membranes involved in 
diffusion are also some of the important factors that can affect the rate of diffusion. 
Pressure contributed by an individual gas in a mixture of gases is called partial 
pressure and is represented as pO
2
 for oxygen and pCO
2
 for carbon dioxide. 
Question 4. What are the major transport mechanisms for CO
2
? Explain. 
Answer:- Transport of Carbon dioxide 
CO
2
 is carried by haemoglobin as carbamino-haemoglobin (about 20-25 per cent). 
This binding is related to the partial pressure of CO
2
. 
pO
2
 is a major factor which could affect this binding. When pCO
2
 is high and pO
2
 is 
low as in the tissues, more binding of carbon dioxide occurs whereas, when the 
pCO
2
 is low and pO
2
 is high as in the alveoli, dissociation of CO
2
 from carbamino-
haemoglobin takes place, i.e., CO
2
 which is bound to haemoglobin from the tissues 
is delivered at the alveoli. 
RBCs contain a very high concentration of the enzyme, carbonic anhydrase and 
minute quantities of the same is present in the plasma too. This enzyme facilitates 
the following reaction in both directions. 
 
 
At the tissue site where partial pressure of CO
2
 is high due to catabolism, 
CO
2
 diffuses into blood (RBCs and plasma) and forms HCO
3
 –and H
+
,. At the 
alveolar site where pCO
2
 is low, the reaction proceeds in the opposite direction 
leading to the formation of CO
2
 and H
2
O. Thus, CO
2
 trapped as bicarbonate at the 
tissue level and transported to the alveoli is released out as CO
2
 . Every 100 ml of 
deoxygenated blood delivers approximately 4 ml of CO
2
 to the alveoli. 
Question 5. What will be the pO
2
 and pCO
2
 in the atmospheric air compared to 
those in the alveolar air ? 
(i) pO
2
 lesser, pCO
2
 higher 
(ii) pO
2
 higher, pCO
2
 lesser 
(iii) pO
2
 higher, pCO
2
 higher 
(iv) pO
2
 lesser, pCO
2
 lesser 
Answer:- (ii) pO
2
 higher will create the pressure gradient to facilitate the movement 
of O
2
 from atmosphere to alveoli and pCO
2
 lesser will create the movement of 
CO
2
 from alveoli to atmosphere. 
Question 6. Explain the process of inspiration under normal conditions. 
Answer: Inspiration is initiated by the contraction of diaphragm which increases the 
volume of thoracic chamber in the antero-posterior axis. The contraction of external 
inter-costal muscles lifts up the ribs and the sternum causing an increase in the 
volume of the thoracic chamber in the dorso-ventral axis. The overall increase in the 
thoracic volume causes a similar increase in pulmonary volume. An increase in 
pulmonary volume decreases the intra-pulmonary pressure to less than the 
atmospheric pressure which forces the air from outside to move into the lungs, i.e., 
inspiration. 
Question 7. How is respiration regulated? 
Answer: Human beings have a significant ability to maintain and moderate the 
respiratory rhythm to suit the demands of the body tissues. This is done by the 
neural system. A specialised centre present in the medulla region of the brain called 
respiratory rhythm centre is primarily responsible for this regulation. Another centre 
present in the pons region of the brain called pneumotaxic centre can moderate the 
Page 3


Breathing And Exchange of Gases 
Question 1. Define vital capacity. What is its significance? 
Answer: Vital Capacity (VC): The maximum volume of air a person can breathe in 
after a forced expiration. This includes ERV (Expiratory Reserve Volume), TV (Tidal 
Volume) and IRV (Inspiratory Reserve Volume) or the maximum volume of air a 
person can breathe out after a forced inspiration. 
Question 2. State the volume of air remaining in the lungs after a normal 
breathing. 
Answer: Functional Residual Capacity (FRC): Volume of air that will remain in the 
lungs after a normal expiration. This includes ERV+RV. 
ERV=1000 to 1100 ml 
RV = 1100 to 1200 ml 
So, FRC = 2100 to 2300 ml 
Question 3. Diffusion of gases occurs in the alveolar region only and not in the 
other parts of respiratory system. Why? 
Answer:- EXCHANGE OF GASES 
Alveoli are the primary sites of exchange of gases. Exchange of gases also occur 
between blood and tissues. O
2
 and CO
2
 are exchanged in these sites by simple 
diffusion mainly based on pressure/concentration gradient. 
Alveolar region is having enough pressure gradient to facilitate diffusion of gases. 
Other regions of the respiratory system don’t have the required pressure gradient. 
Solubility of the gases as well as the thickness of the membranes involved in 
diffusion are also some of the important factors that can affect the rate of diffusion. 
Pressure contributed by an individual gas in a mixture of gases is called partial 
pressure and is represented as pO
2
 for oxygen and pCO
2
 for carbon dioxide. 
Question 4. What are the major transport mechanisms for CO
2
? Explain. 
Answer:- Transport of Carbon dioxide 
CO
2
 is carried by haemoglobin as carbamino-haemoglobin (about 20-25 per cent). 
This binding is related to the partial pressure of CO
2
. 
pO
2
 is a major factor which could affect this binding. When pCO
2
 is high and pO
2
 is 
low as in the tissues, more binding of carbon dioxide occurs whereas, when the 
pCO
2
 is low and pO
2
 is high as in the alveoli, dissociation of CO
2
 from carbamino-
haemoglobin takes place, i.e., CO
2
 which is bound to haemoglobin from the tissues 
is delivered at the alveoli. 
RBCs contain a very high concentration of the enzyme, carbonic anhydrase and 
minute quantities of the same is present in the plasma too. This enzyme facilitates 
the following reaction in both directions. 
 
 
At the tissue site where partial pressure of CO
2
 is high due to catabolism, 
CO
2
 diffuses into blood (RBCs and plasma) and forms HCO
3
 –and H
+
,. At the 
alveolar site where pCO
2
 is low, the reaction proceeds in the opposite direction 
leading to the formation of CO
2
 and H
2
O. Thus, CO
2
 trapped as bicarbonate at the 
tissue level and transported to the alveoli is released out as CO
2
 . Every 100 ml of 
deoxygenated blood delivers approximately 4 ml of CO
2
 to the alveoli. 
Question 5. What will be the pO
2
 and pCO
2
 in the atmospheric air compared to 
those in the alveolar air ? 
(i) pO
2
 lesser, pCO
2
 higher 
(ii) pO
2
 higher, pCO
2
 lesser 
(iii) pO
2
 higher, pCO
2
 higher 
(iv) pO
2
 lesser, pCO
2
 lesser 
Answer:- (ii) pO
2
 higher will create the pressure gradient to facilitate the movement 
of O
2
 from atmosphere to alveoli and pCO
2
 lesser will create the movement of 
CO
2
 from alveoli to atmosphere. 
Question 6. Explain the process of inspiration under normal conditions. 
Answer: Inspiration is initiated by the contraction of diaphragm which increases the 
volume of thoracic chamber in the antero-posterior axis. The contraction of external 
inter-costal muscles lifts up the ribs and the sternum causing an increase in the 
volume of the thoracic chamber in the dorso-ventral axis. The overall increase in the 
thoracic volume causes a similar increase in pulmonary volume. An increase in 
pulmonary volume decreases the intra-pulmonary pressure to less than the 
atmospheric pressure which forces the air from outside to move into the lungs, i.e., 
inspiration. 
Question 7. How is respiration regulated? 
Answer: Human beings have a significant ability to maintain and moderate the 
respiratory rhythm to suit the demands of the body tissues. This is done by the 
neural system. A specialised centre present in the medulla region of the brain called 
respiratory rhythm centre is primarily responsible for this regulation. 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. A chemo-sensitive 
area is situated adjacent to the rhythm centre which is highly sensitive to CO
2
 and 
hydrogen ions. Increase in these substances can activate this centre, which in turn 
can signal the rhythm centre to make necessary adjustments in the respiratory 
process by which these substances can be eliminated. Receptors associated with 
aortic arch and carotid artery also can recognize changes in CO
2
 and 
H
+
 concentration and send necessary signals to the rhythm centre for remedial 
actions. The role of oxygen in the regulation of respiratory rhythm is quite 
insignificant. 
Question 8. What is the effect of pCO
2
 on oxygen transport? 
Answer: Binding of oxygen with haemoglobin is primarily related to partial pressure 
of O
2
. Partial pressure of CO
2
, hydrogen ion concentration and temperature are the 
other factors which can interfere with this binding. Increased partial pressure of 
CO
2
 can increase haemoglobin’s affinity towards oxygen and vice-versa is also true. 
9. What happens to the respiratory process in a man going up a hill? 
Answer: When a man is going uphill or doing some strenuous exercise then there is 
more consumption of oxygen. This decreases the partial pressure of oxygen in 
haemogloin resulting in more demand of haemoglobin. As a result there is an 
increased breathing rate to fill the gap. 
Question 10. What is the site of gaseous exchange in an insect? 
Answer: Insect respiration is accomplished without lungs using a system of internal 
tubes and sacs through which gases either diffuse or are actively pumped, delivering 
oxygen directly to tissues that need oxygen (see invertebrate trachea). Since oxygen 
is delivered directly, the circulatory system is not used to carry oxygen, and is 
therefore greatly reduced; it has no closed vessels (i.e., no veins or arteries), 
consisting of little more than a single, perforated dorsal tube which pulses 
peristaltically, and in doing so helps circulate the hemolymph inside the body cavity. 
Air is taken in through spiracles, openings on the sides of the abdomen. There are 
many different patterns of gas exchange demonstrated by different groups of insects. 
Gas exchange patterns in insects can range from continuous, diffusive ventilation, to 
discontinuous gas exchange. 
Question 11. Define oxygen dissociation curve. Can you suggest any reason 
for its sigmoidal pattern? 
Answer: Blood is the medium of transport for O
2
 and CO
2
. About 97 per cent of O
2
 is 
transported by RBCs in the blood. The remaining 3 per cent of O
2
 is carried in a 
dissolved state through the plasma. Nearly 20-25 per cent of CO
2
 is transported by 
RBCs whereas 70 per cent of it is carried as bicarbonate. About 7 per cent of CO
2
 is 
carried in a dissolved state through plasma. 
Page 4


Breathing And Exchange of Gases 
Question 1. Define vital capacity. What is its significance? 
Answer: Vital Capacity (VC): The maximum volume of air a person can breathe in 
after a forced expiration. This includes ERV (Expiratory Reserve Volume), TV (Tidal 
Volume) and IRV (Inspiratory Reserve Volume) or the maximum volume of air a 
person can breathe out after a forced inspiration. 
Question 2. State the volume of air remaining in the lungs after a normal 
breathing. 
Answer: Functional Residual Capacity (FRC): Volume of air that will remain in the 
lungs after a normal expiration. This includes ERV+RV. 
ERV=1000 to 1100 ml 
RV = 1100 to 1200 ml 
So, FRC = 2100 to 2300 ml 
Question 3. Diffusion of gases occurs in the alveolar region only and not in the 
other parts of respiratory system. Why? 
Answer:- EXCHANGE OF GASES 
Alveoli are the primary sites of exchange of gases. Exchange of gases also occur 
between blood and tissues. O
2
 and CO
2
 are exchanged in these sites by simple 
diffusion mainly based on pressure/concentration gradient. 
Alveolar region is having enough pressure gradient to facilitate diffusion of gases. 
Other regions of the respiratory system don’t have the required pressure gradient. 
Solubility of the gases as well as the thickness of the membranes involved in 
diffusion are also some of the important factors that can affect the rate of diffusion. 
Pressure contributed by an individual gas in a mixture of gases is called partial 
pressure and is represented as pO
2
 for oxygen and pCO
2
 for carbon dioxide. 
Question 4. What are the major transport mechanisms for CO
2
? Explain. 
Answer:- Transport of Carbon dioxide 
CO
2
 is carried by haemoglobin as carbamino-haemoglobin (about 20-25 per cent). 
This binding is related to the partial pressure of CO
2
. 
pO
2
 is a major factor which could affect this binding. When pCO
2
 is high and pO
2
 is 
low as in the tissues, more binding of carbon dioxide occurs whereas, when the 
pCO
2
 is low and pO
2
 is high as in the alveoli, dissociation of CO
2
 from carbamino-
haemoglobin takes place, i.e., CO
2
 which is bound to haemoglobin from the tissues 
is delivered at the alveoli. 
RBCs contain a very high concentration of the enzyme, carbonic anhydrase and 
minute quantities of the same is present in the plasma too. This enzyme facilitates 
the following reaction in both directions. 
 
 
At the tissue site where partial pressure of CO
2
 is high due to catabolism, 
CO
2
 diffuses into blood (RBCs and plasma) and forms HCO
3
 –and H
+
,. At the 
alveolar site where pCO
2
 is low, the reaction proceeds in the opposite direction 
leading to the formation of CO
2
 and H
2
O. Thus, CO
2
 trapped as bicarbonate at the 
tissue level and transported to the alveoli is released out as CO
2
 . Every 100 ml of 
deoxygenated blood delivers approximately 4 ml of CO
2
 to the alveoli. 
Question 5. What will be the pO
2
 and pCO
2
 in the atmospheric air compared to 
those in the alveolar air ? 
(i) pO
2
 lesser, pCO
2
 higher 
(ii) pO
2
 higher, pCO
2
 lesser 
(iii) pO
2
 higher, pCO
2
 higher 
(iv) pO
2
 lesser, pCO
2
 lesser 
Answer:- (ii) pO
2
 higher will create the pressure gradient to facilitate the movement 
of O
2
 from atmosphere to alveoli and pCO
2
 lesser will create the movement of 
CO
2
 from alveoli to atmosphere. 
Question 6. Explain the process of inspiration under normal conditions. 
Answer: Inspiration is initiated by the contraction of diaphragm which increases the 
volume of thoracic chamber in the antero-posterior axis. The contraction of external 
inter-costal muscles lifts up the ribs and the sternum causing an increase in the 
volume of the thoracic chamber in the dorso-ventral axis. The overall increase in the 
thoracic volume causes a similar increase in pulmonary volume. An increase in 
pulmonary volume decreases the intra-pulmonary pressure to less than the 
atmospheric pressure which forces the air from outside to move into the lungs, i.e., 
inspiration. 
Question 7. How is respiration regulated? 
Answer: Human beings have a significant ability to maintain and moderate the 
respiratory rhythm to suit the demands of the body tissues. This is done by the 
neural system. A specialised centre present in the medulla region of the brain called 
respiratory rhythm centre is primarily responsible for this regulation. 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. A chemo-sensitive 
area is situated adjacent to the rhythm centre which is highly sensitive to CO
2
 and 
hydrogen ions. Increase in these substances can activate this centre, which in turn 
can signal the rhythm centre to make necessary adjustments in the respiratory 
process by which these substances can be eliminated. Receptors associated with 
aortic arch and carotid artery also can recognize changes in CO
2
 and 
H
+
 concentration and send necessary signals to the rhythm centre for remedial 
actions. The role of oxygen in the regulation of respiratory rhythm is quite 
insignificant. 
Question 8. What is the effect of pCO
2
 on oxygen transport? 
Answer: Binding of oxygen with haemoglobin is primarily related to partial pressure 
of O
2
. Partial pressure of CO
2
, hydrogen ion concentration and temperature are the 
other factors which can interfere with this binding. Increased partial pressure of 
CO
2
 can increase haemoglobin’s affinity towards oxygen and vice-versa is also true. 
9. What happens to the respiratory process in a man going up a hill? 
Answer: When a man is going uphill or doing some strenuous exercise then there is 
more consumption of oxygen. This decreases the partial pressure of oxygen in 
haemogloin resulting in more demand of haemoglobin. As a result there is an 
increased breathing rate to fill the gap. 
Question 10. What is the site of gaseous exchange in an insect? 
Answer: Insect respiration is accomplished without lungs using a system of internal 
tubes and sacs through which gases either diffuse or are actively pumped, delivering 
oxygen directly to tissues that need oxygen (see invertebrate trachea). Since oxygen 
is delivered directly, the circulatory system is not used to carry oxygen, and is 
therefore greatly reduced; it has no closed vessels (i.e., no veins or arteries), 
consisting of little more than a single, perforated dorsal tube which pulses 
peristaltically, and in doing so helps circulate the hemolymph inside the body cavity. 
Air is taken in through spiracles, openings on the sides of the abdomen. There are 
many different patterns of gas exchange demonstrated by different groups of insects. 
Gas exchange patterns in insects can range from continuous, diffusive ventilation, to 
discontinuous gas exchange. 
Question 11. Define oxygen dissociation curve. Can you suggest any reason 
for its sigmoidal pattern? 
Answer: Blood is the medium of transport for O
2
 and CO
2
. About 97 per cent of O
2
 is 
transported by RBCs in the blood. The remaining 3 per cent of O
2
 is carried in a 
dissolved state through the plasma. Nearly 20-25 per cent of CO
2
 is transported by 
RBCs whereas 70 per cent of it is carried as bicarbonate. About 7 per cent of CO
2
 is 
carried in a dissolved state through plasma. 
 
 
Haemoglobin is a red coloured iron containing pigment present in the RBCs. O
2
 can 
bind with haemoglobin in a reversible manner to form oxyhaemoglobin. Each 
haemoglobin molecule can carry a maximum of four molecules of O
2
. Binding of 
oxygen with haemoglobin is primarily related to partial pressure of O
2
. Partial 
pressure of CO
2
, hydrogen ion concentration and temperature are the other factors 
which can interfere with this binding. A sigmoid curve is obtained when percentage 
saturation of haemoglobin with O
2
 is plotted against the pO
2
. This curve is called the 
Oxygen dissociation curve and is highly useful in studying the effect of factors like 
pCO
2
, H
+
 concentration, etc., on binding of O
2
 with haemoglobin. 
Question 12. Have you heard about hypoxia? Try to gather information about 
it, and discuss with your friends. 
Answer: Hypoxia is a pathological condition in which the body as a whole 
(generalized hypoxia) or a region of the body (tissue hypoxia) is deprived of 
adequate oxygen supply. Variations in arterial oxygen concentrations can be part of 
the normal physiology, for example, during strenuous physical exercise. A mismatch 
between oxygen supply and its demand at the cellular level may result in a hypoxic 
condition. Hypoxia in which there is complete deprivation of oxygen supply is 
referred to as anoxia. 
Question 13. Distinguish between 
(a) IRV and ERV 
(b) Inspiratory capacity and Expiratory capacity. 
(c) Vital capacity and Total lung capacity. 
Answer: (a) Inspiratory Reserve Volume (IRV): Additional volume of air, a person 
can inspire by a forcible inspiration. This averages 2500 ml to 3000 ml. 
Page 5


Breathing And Exchange of Gases 
Question 1. Define vital capacity. What is its significance? 
Answer: Vital Capacity (VC): The maximum volume of air a person can breathe in 
after a forced expiration. This includes ERV (Expiratory Reserve Volume), TV (Tidal 
Volume) and IRV (Inspiratory Reserve Volume) or the maximum volume of air a 
person can breathe out after a forced inspiration. 
Question 2. State the volume of air remaining in the lungs after a normal 
breathing. 
Answer: Functional Residual Capacity (FRC): Volume of air that will remain in the 
lungs after a normal expiration. This includes ERV+RV. 
ERV=1000 to 1100 ml 
RV = 1100 to 1200 ml 
So, FRC = 2100 to 2300 ml 
Question 3. Diffusion of gases occurs in the alveolar region only and not in the 
other parts of respiratory system. Why? 
Answer:- EXCHANGE OF GASES 
Alveoli are the primary sites of exchange of gases. Exchange of gases also occur 
between blood and tissues. O
2
 and CO
2
 are exchanged in these sites by simple 
diffusion mainly based on pressure/concentration gradient. 
Alveolar region is having enough pressure gradient to facilitate diffusion of gases. 
Other regions of the respiratory system don’t have the required pressure gradient. 
Solubility of the gases as well as the thickness of the membranes involved in 
diffusion are also some of the important factors that can affect the rate of diffusion. 
Pressure contributed by an individual gas in a mixture of gases is called partial 
pressure and is represented as pO
2
 for oxygen and pCO
2
 for carbon dioxide. 
Question 4. What are the major transport mechanisms for CO
2
? Explain. 
Answer:- Transport of Carbon dioxide 
CO
2
 is carried by haemoglobin as carbamino-haemoglobin (about 20-25 per cent). 
This binding is related to the partial pressure of CO
2
. 
pO
2
 is a major factor which could affect this binding. When pCO
2
 is high and pO
2
 is 
low as in the tissues, more binding of carbon dioxide occurs whereas, when the 
pCO
2
 is low and pO
2
 is high as in the alveoli, dissociation of CO
2
 from carbamino-
haemoglobin takes place, i.e., CO
2
 which is bound to haemoglobin from the tissues 
is delivered at the alveoli. 
RBCs contain a very high concentration of the enzyme, carbonic anhydrase and 
minute quantities of the same is present in the plasma too. This enzyme facilitates 
the following reaction in both directions. 
 
 
At the tissue site where partial pressure of CO
2
 is high due to catabolism, 
CO
2
 diffuses into blood (RBCs and plasma) and forms HCO
3
 –and H
+
,. At the 
alveolar site where pCO
2
 is low, the reaction proceeds in the opposite direction 
leading to the formation of CO
2
 and H
2
O. Thus, CO
2
 trapped as bicarbonate at the 
tissue level and transported to the alveoli is released out as CO
2
 . Every 100 ml of 
deoxygenated blood delivers approximately 4 ml of CO
2
 to the alveoli. 
Question 5. What will be the pO
2
 and pCO
2
 in the atmospheric air compared to 
those in the alveolar air ? 
(i) pO
2
 lesser, pCO
2
 higher 
(ii) pO
2
 higher, pCO
2
 lesser 
(iii) pO
2
 higher, pCO
2
 higher 
(iv) pO
2
 lesser, pCO
2
 lesser 
Answer:- (ii) pO
2
 higher will create the pressure gradient to facilitate the movement 
of O
2
 from atmosphere to alveoli and pCO
2
 lesser will create the movement of 
CO
2
 from alveoli to atmosphere. 
Question 6. Explain the process of inspiration under normal conditions. 
Answer: Inspiration is initiated by the contraction of diaphragm which increases the 
volume of thoracic chamber in the antero-posterior axis. The contraction of external 
inter-costal muscles lifts up the ribs and the sternum causing an increase in the 
volume of the thoracic chamber in the dorso-ventral axis. The overall increase in the 
thoracic volume causes a similar increase in pulmonary volume. An increase in 
pulmonary volume decreases the intra-pulmonary pressure to less than the 
atmospheric pressure which forces the air from outside to move into the lungs, i.e., 
inspiration. 
Question 7. How is respiration regulated? 
Answer: Human beings have a significant ability to maintain and moderate the 
respiratory rhythm to suit the demands of the body tissues. This is done by the 
neural system. A specialised centre present in the medulla region of the brain called 
respiratory rhythm centre is primarily responsible for this regulation. 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. A chemo-sensitive 
area is situated adjacent to the rhythm centre which is highly sensitive to CO
2
 and 
hydrogen ions. Increase in these substances can activate this centre, which in turn 
can signal the rhythm centre to make necessary adjustments in the respiratory 
process by which these substances can be eliminated. Receptors associated with 
aortic arch and carotid artery also can recognize changes in CO
2
 and 
H
+
 concentration and send necessary signals to the rhythm centre for remedial 
actions. The role of oxygen in the regulation of respiratory rhythm is quite 
insignificant. 
Question 8. What is the effect of pCO
2
 on oxygen transport? 
Answer: Binding of oxygen with haemoglobin is primarily related to partial pressure 
of O
2
. Partial pressure of CO
2
, hydrogen ion concentration and temperature are the 
other factors which can interfere with this binding. Increased partial pressure of 
CO
2
 can increase haemoglobin’s affinity towards oxygen and vice-versa is also true. 
9. What happens to the respiratory process in a man going up a hill? 
Answer: When a man is going uphill or doing some strenuous exercise then there is 
more consumption of oxygen. This decreases the partial pressure of oxygen in 
haemogloin resulting in more demand of haemoglobin. As a result there is an 
increased breathing rate to fill the gap. 
Question 10. What is the site of gaseous exchange in an insect? 
Answer: Insect respiration is accomplished without lungs using a system of internal 
tubes and sacs through which gases either diffuse or are actively pumped, delivering 
oxygen directly to tissues that need oxygen (see invertebrate trachea). Since oxygen 
is delivered directly, the circulatory system is not used to carry oxygen, and is 
therefore greatly reduced; it has no closed vessels (i.e., no veins or arteries), 
consisting of little more than a single, perforated dorsal tube which pulses 
peristaltically, and in doing so helps circulate the hemolymph inside the body cavity. 
Air is taken in through spiracles, openings on the sides of the abdomen. There are 
many different patterns of gas exchange demonstrated by different groups of insects. 
Gas exchange patterns in insects can range from continuous, diffusive ventilation, to 
discontinuous gas exchange. 
Question 11. Define oxygen dissociation curve. Can you suggest any reason 
for its sigmoidal pattern? 
Answer: Blood is the medium of transport for O
2
 and CO
2
. About 97 per cent of O
2
 is 
transported by RBCs in the blood. The remaining 3 per cent of O
2
 is carried in a 
dissolved state through the plasma. Nearly 20-25 per cent of CO
2
 is transported by 
RBCs whereas 70 per cent of it is carried as bicarbonate. About 7 per cent of CO
2
 is 
carried in a dissolved state through plasma. 
 
 
Haemoglobin is a red coloured iron containing pigment present in the RBCs. O
2
 can 
bind with haemoglobin in a reversible manner to form oxyhaemoglobin. Each 
haemoglobin molecule can carry a maximum of four molecules of O
2
. Binding of 
oxygen with haemoglobin is primarily related to partial pressure of O
2
. Partial 
pressure of CO
2
, hydrogen ion concentration and temperature are the other factors 
which can interfere with this binding. A sigmoid curve is obtained when percentage 
saturation of haemoglobin with O
2
 is plotted against the pO
2
. This curve is called the 
Oxygen dissociation curve and is highly useful in studying the effect of factors like 
pCO
2
, H
+
 concentration, etc., on binding of O
2
 with haemoglobin. 
Question 12. Have you heard about hypoxia? Try to gather information about 
it, and discuss with your friends. 
Answer: Hypoxia is a pathological condition in which the body as a whole 
(generalized hypoxia) or a region of the body (tissue hypoxia) is deprived of 
adequate oxygen supply. Variations in arterial oxygen concentrations can be part of 
the normal physiology, for example, during strenuous physical exercise. A mismatch 
between oxygen supply and its demand at the cellular level may result in a hypoxic 
condition. Hypoxia in which there is complete deprivation of oxygen supply is 
referred to as anoxia. 
Question 13. Distinguish between 
(a) IRV and ERV 
(b) Inspiratory capacity and Expiratory capacity. 
(c) Vital capacity and Total lung capacity. 
Answer: (a) Inspiratory Reserve Volume (IRV): Additional volume of air, a person 
can inspire by a forcible inspiration. This averages 2500 ml to 3000 ml. 
Expiratory Reserve Volume (ERV): Additional volume of air, a person can expire 
by a forcible expiration. This averages 1000 ml to 1100 ml. 
(b) Inspiratory Capacity (IC): Total volume of air a person can inspire after a 
normal expiration. This includes tidal volume and inspiratory reserve volume 
(TV+IRV). 
Expiratory Capacity (EC): Total volume of air a person can expire after a normal 
inspiration. This includes tidal volume and expiratory reserve volume (TV+ERV). 
(c) Vital Capacity (VC): The maximum volume of air 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. 
Total Lung Capacity: 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. 
Question 14. What is Tidal volume? Find out the Tidal volume (approximate 
value) for a healthy human in an hour. 
Answer: Tidal Volume (TV): Volume of air inspired or expired during a normal 
respiration. It is approx. 500 ml., i.e., a healthy man can inspire or expire 
approximately 6000 to 8000 ml of air per minute (12X500=6000). 
 
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