CBSE Class 11 Biology Breathing and Exchange of Gases MCQs

Question. When about 1200 mL air is in the lungs after forceful expiration, it is called
a) residual volume
b) inspiratory reserve volume
c) vital capacity
d) tidal volume.

Answer : A

Question. When the blood contains a high percentage of CO2 and a very low percentage of O2, the breathing stops and the person becomes unconscious. This condition is known as
a) suffocation
b) asphyxia
c) emphysema
d) eupnea.

Answer : B

Question. After forceful inspiration, the amount of air that can be breathed out by maximum forced expiration is equal to
a) Inspiratory Reserve Volume (IRV) +Expiratory Reserve Volume (ERV) + Tidal Volume (TV) + Residual Volume (RV)
b) IRV + RV + ERV
c) IRV + TV + ERV
d) TV + RV + ERV.

Answer : C

Question. Among mammals, the efficiency of ventilation of lungs as compared to reptiles and birds is better developed by the presence of
a) ribs and costal muscles
b) only ribs
c) only costal muscles
d) diaphragm.

Answer : D

Question. Pneumotaxic centre is present in
a) pons
b) medulla
c) cerebrum
d) lungs.

Answer : A

Question. In oxygen dissociation curve x-axis and y-axis represents.
a) x-axis—partial pressure of oxygen
y-axis—percentage saturation of Hb with oxygen
b) x - a x i s — p e r c e n t a g e s a t u r a t i o n o f haemoglobin
y-axis—partial pressure of oxygen
c) x-axis—partial pressure of CO2
y - a x i s — percentagesaturation of oxyhaemoglobin with oxygen
d) x-axis—partial pressure of CO2
y-axis—partial pressure of oxygen.

Answer : A

Question. Factor helps in formation of oxyhaemoglobin in alveoli is
a) high pCO2
b) high pO2
c) higher H+ concentration
d) all of these.

Answer : B

Question. Cartilaginous rings in trachea are incomplete at which surface?
a) Dorsal
b) Ventral
c) Lateral
d) Ventrolateral

Answer : A

Question. Between breaths the intrapleural pressure is approximately ___ mmHg less than atmospheric pressure.
a) 1
b) 4
c) 8
d) 10

Answer : B

Question. Oxyhaemoglobin is converted into haemoglobin during the internal respiration because
a) an enzyme splits oxyhaemoglobin
b) oxygen tension in tissue is less than capillary blood reaching tissue
c) CO2 tension is low in blood that reaches tissue
d) oxyhaemoglobin is unstable.

Answer : D

Question : Bulk of carbon dioxide (CO2) released from body tissues into the blood is present as
a) bicarbonate in blood plasma and RBCs
b) 70% carbamino- haemoglobin and 30% as bicarbonate
c) carbamino-haemoglobin in RBCs
d) free CO2 in blood plasma

Answer : A

Question : A large proportion of oxygen is left unused in the human blood even after its uptake by the body tissues. This O2
a) acts as a reserve during muscular exercise
b) is enough to keep oxyhaemoglobin saturation at 96%
c) helps in releasing more O2 to the epithelial tissues
d) None of these

Answer : A

Question : Oxygen dissociation curve of haemoglobin is
a) Sigmoid
b) Hyperbolic
c) Hypobolic
d) Linear
Answer : Sigmoid

Question : Which one of the following organs in the human body is most affected due to shortage of oxygen?
a) Brain
b) Kidney
c) Skin
d) Intestine
Answer : Brain

Question : When CO2 concentration in blood increases, breathing becomes
a) faster and deeper
b) slow and deep
c) there is no effect on breathing
d) shallower and slow
Answer : faster and deeper

Question : The largest quantity of air that can be expired after a maximal inspiratory effort is called
a) vital capacity
b) residual volume
c) tidal volume
d) total lung volume
Answer : vital capacity

Question : Which one of the following statements is incorrect ?
a) In insects, circulating body fluids serve to distribute oxygen to tissues
b) The principle of counter current flow facilitates efficient respiration in gills of fishes
c) The residual air in lungs slightly decreases the efficiency of respriration in mammals.
d) None of these
Answer : In insects, circulating body fluids serve to distribute oxygen to tissues

Question : Emphysema developes mainly because of
a) Spasm of the smooth muscles of bronchioles
b) Cigarette smoking
c) Inflammation of the alveoli
d) Allergy or hypersensitisation
Answer : Spasm of the smooth muscles of bronchioles

Question : During inspiration the diaphragm
a) contracts and flattens
b) relaxes to become dome-shaped
c) shows no change
d) None of these
Answer : contracts and flattens

Question : The volume of air breathed in and out during normal breathing is called
a) Tidal volume
b) Explratory reserve volume
c) Vital capacity
d) None of these
Answer : Tidal volume

Question : What would happen if human blood becomes acidic (low pH)
a) Oxygen carrying capacity of haemoglobin decreases
b) RBCs count increases
c) RBCs count decreases
d) Oxygen carying capacity of haemoglobin increases
Answer : Oxygen carrying capacity of haemoglobin decreases

Question : Even when there is no air in it, human trachea does not collapse due to presence of
a) Cartilaginous rings
b) Turgid pressure
c) Bony rings
d) Chitinous rings
Answer : Cartilaginous rings

Question : The structure which does not contribute to the breathing movements in mammals is
a) Larynx
b) Diaphragm
c) Ribs
d) Intercostal muscles
Answer : Larynx

Question : In emphysema
a) Gas exchange area of lungs is reduced
b) Gas exchange area of lungs is increased
c) Trachea gets narrowed
d) Larynx is permanently closed
Answer : Gas exchange area of lungs is reduced

Question : Which of the following changes occur in diaphragm and intercostal muscles when expiration of air takes place?
a) External intercostal muscles and diaphargm relax
b) External intercostal muscles and diaphargm contract
c) External intercostal muscles contract and diaphargm relaxes
d) External intercostal muscles relax and diaphargm contracts
Answer : External intercostal muscles and diaphargm relax

Question : When you exhale, the diaphragm
a) relaxes and arches
b) relaxes and flattens.
c) contracts and arches
d) contracts and flattens
Answer : relaxes and arches

Question : Smoking destroys the cilia in the respiratory passageways. This
a) makes it harder to keep the lungs clean
b) slows blood flow through lung blood vessels
c) decreases the surface area for respiration.
d) makes it harder to move air in and out of the lungs
Answer : makes it harder to keep the lungs clean

Question : Gas flows into the lungs of mammals during inspiration because
a) The pressure in the lungs falls below atmospheric pressure
b) The pressure in the lungs rises above atmospheric pressure.
c) The volume of the lungs decreases
d) The diaphragm moves upward toward the lungs
Answer : The pressure in the lungs falls below atmospheric pressure

Question : The function of the mucus elevator in the mammalian respiratory system is to
a) trap and remove particulate matter that has entered the respiratory system.
b) stimulate contraction of rib musculature during forcible exhalation
c) produce negative pressure during inhalation
d) move surfactant from the bronchi to the alveoli
Answer : trap and remove particulate matter that has entered the respiratory system.

Question : During inspiration, the air is brought into the lungs by the working of the thoracoabdominal pump whereby the
a) all of the above
b) abdominal muscles relax
c) chest muscles pull the ribs up and out to widen the thoracic cavity
d) diaphragm contracts to lengthen the thoracic cavity
Answer : all of the above

Question : The alveolar epithelium in the lung is
a) non-ciliated columnar
b) non-ciliated squamous
c) ciliated columnar
d) ciliated squamous
Answer : B

Question : Skin is an accessory organ of respiration in
a) human
b) frog
c) rabbit
d) lizard
Answer : B

Question : Carbon dioxide is transported from tissues to respiratory surface by only
a) plasma and erythrocytes
b) plasma
c) erythrocytes
d) erythrocytes and leucocytes
Answer : A

Question : Air is breathed through
a) trachea—lungs—larynx—pharynx—alveoli
b) nose—larynx—pharynx—bronchus—alveoli—bronchioles
c) nostrils—pharynx—larynx—trachea—bronchi—bronchioles—alveoli
d) nose — mouth — lungs
Answer : C

Question : Oxygen dissociation curve of haemoglobin is
a) sigmoid
b) hyperbolic
c) linear
d) hypobolic
Answer : A

Question : Although much CO2 is carried in blood, yet blood does not become acidic, because
a) it is absorbed by the leucocytes
b) blood buffers play an important role in CO2 transport
c) it combines with water to form H2CO3 which is neutralized by Na2CO3
d) it is continuously diffused through tissues and is not allowed to accumulate
Answer : B

Question : The carbon dioxide is transported via blood to lungs as
a) dissolved in blood plasma
b) in the form of carbonic acid only
c) in combination with haemoglobin only
d) carbaminohaemoglobin and as carbonic acid
Answer : D

Question : The quantity 1500 mL in the respiratory volumes of a normal human adult refers to
a) maximum air that can be breathed in and breathed out
b) residual volume
c) expiratory reserve volume
d) total lung capacity
Answer : B

Question : In alveoli of the lungs, the air at the site of gas exchange, is separated from the blood by
a) alveolar epithelium only
b) alveolar epithelium and capillary endothelium
c) alveolar epithelium, capillary endothelium and tunica adventitia
d) alveolar epithelium, capillary endothelium, a thin layer of tunica media and tunica adventitia
Answer : B

Question : The exchange of gases in the alveoli of the lungs takes place by
a) simple diffusion
b) osmosis
c) active transport
d) passive transport
Answer : A

Question : Which one of the following organs in the human body is most affected due to shortage of oxygen?
a) Intestine
b) Skin
c) Kidney
d) Brain
Answer : D

Question : The process of migration of chloride ions from plasma to RBC and of carbonate ions from RBC to plasma is
a) chloride shift
b) ionic shift
c) atomic shift
d) Na+ pump
Answer : A

Question : When CO2 concentration in blood increases, breathing becomes
a) shallower and slow
b) there is no effect on breathing
c) slow and deep
d) faster and deeper
Answer : D

Question : Blood analysis of a patient reveals an unusually high quantity of carboxyhaemoglobin content. Which of the following conclusions is most likely to be correct?
a) The patient has been inhaling polluted air containing unusually high content of carbon disulphide
b) The patient has been inhaling polluted air containing unusually high content of chloroform
c) The patient has been inhaling polluted air containing unusually high content of carbon dioxide
d) The patient has been inhaling polluted air containing unusually high content of carbon monoxide
Answer : D

Question : People living at sea level have around 5 million RBC per cubic millimeter of their blood whereas those living at an altitude of 5400 metre have around 8 million. This is because at high altitude
a) atmospheric O2 level is less and hence,more RBCs are needed to absorb the required amount of O2 to survive
b) there is more UV radiation which enhances RBC production
c) people eat more nutritive food, therefore, more RBCs are formed
d) people get pollution-free air to breathe and more oxygen is available
Answer : A

Question : What is the vital capacity of our lungs?
a) Inspiratory reserve volume plus tidal volume
b) Total lung capacity minus expiratory reserve volume
c) Inspiratory reserve volume plus expiratory reserve volume
d) Total lung capacity minus residual volume
Answer : D

Question : The haemoglobin of a human foetus
a) has a lower affinity for oxygen than that of the adult
b) its affinity for oxygen is the same as that of an adult
c) has only 2 protein subunits instead of 4
d) has a higher affinity for oxygen than that of an adult
Answer : D

Question : Which one of the following is a possibility for most of us in regard to breathing, by making a conscious effort ?
a) The lungs can be made fully empty by forcefully breathing out all air from them
b) One can breathe out air totally without oxygen.
c) One can breathe out air through eustachian tubes by closing both the nose and the mouth
d) One can consciously breath in and breath out by moving the diaphragm alone, without moving the ribs at all.
Answer : A

Question : A large proportion of oxygen is left unused in the human blood even after its uptake by the body tissues. This O2
a) Acts as a reserve during muscular exercise
b) Raises the pCO2 of blood to 75 mm of Hg.
c) Is enough to keep oxyhaemoglobin sturation at 96%
d) Helps in releasing more O2 to the epithelial tissues
Answer : A

Question : Two friends are eating together on a dining table. One of them suddenly starts coughing while swallowing some food. This coughing would have been due to improper movement of
a) Epiglottis
b) Diaphragm
c) Neck
d) Tongue

Answer : A

Assertion & Reason Based MCQ For question numbers 51-60, two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Question. Assertion : Bronchitis is characterised by regular cough with greenish yellow sputum.
Reason : Bronchitis is due to overgrowth of goblet cells lining of bronchi.
Answer : B

Question. Assertion : The dorsal respiratory group (DRG) present in the dorsal portion of medulla oblongata mainly causes expiration.
Reason : The ventral respiratory group (VRG) on the ventrolateral part of medulla oblongata cause either inspiration or expiration.
Answer : D

Question. Assertion : Emphysema is a chronic disorder in which alveolar walls are damaged.
Reason : Emphysema is closely related to cigarette smoking.
Answer : B

Question. Assertion : Respiratory gas goes from higher partial pressure region to the region of lower partial pressure.
Reason : Respiratory gas exchange occurs through osmosis.
Answer : C

Question. Assertion : During inspiration, the volume of thorax increases.
Reason : This happens due to the relaxation of diaphragm and inspiratory muscles.
Answer : C

Question. Assertion : Vital capacity is higher in athletes than non - athletes.
Reason : Vital capacity is about 3.5 - 4.5 litres in a normal adult person.
Answer : B

Question. Assertion : Aerobic animals are not truely aerobic.
Reason : They produce lactic acid anaerobically.
Answer : A

Question. Assertion : Oxygenation of blood promotes the release of carbon dioxide from the blood in the lungs.
Reason : Carbon dioxide is carried as bicarbonates in erythrocytes of blood.
Answer : B

Question. Assertion : During expiration, volume of thorax decreases and air is expelled out.
Reason : This happens due to the contraction of expiratory muscles.
Answer : A

Question. Assertion : Extra oxygen consumption in human body is known as oxygen debt.
Reason : The extra oxygen is required by the body to oxidise the accumulated lactic acid produced during strenuous exercise.
Answer : A

Short Answer Type Questions 

Question. What is carbonic anhydrase? List the major forms in which the carbon dioxide is transported in the blood. 
Answer. Carbonic anhydrase is an enzyme present in erythrocytes that reversibly catalyses the conversion of carbon dioxide and water to carbonic acid. Nearly 20–25 percent of CO2 is transported by haemoglobin of RBCs, as carbaminohaemoglobin. This binding is related to the partial pressure of CO2. About 70 percent of it is carried as bicarbonate ion in plasma and about 7 percent of CO2 is carried in a dissolved state through plasma, by haemoglobin.

Question. The following figure shows an alveolus with a capillary in close contact. (a) Identify the gases A and B. (b) Name the process by which these gases move between blood and the alveolus.
Answer. (a) Gas A is carbon dioxide and Gas B is oxygen. (b) The process by which gases move between blood and alveolus is diffusion. Gases always diffuse from region of higher to a lower concentration.

Question. How does the exchange of gases occur between the alveoli and blood? Diagrammatically show the section of alveolus and pulmonary blood capillary. 
Answer. The exchange of gases, i.e., oxygen and carbon dioxide between lung alveoli and pulmonary capillaries is known as external respiration. The respiratory membrane is a thin wall of alveoli that is richly supplied with network of blood capillaries. This membrane has a limit of gaseous exchange between alveoli and pulmonary blood, called diffusing capacity. Diffusing capacity is the volume of gas which diffuses through the membrane per minute for a pressure difference of 1 mmHg. The partial pressure of oxygen pO2 in the alveoli is higher (104 mmHg) than that in deoxygenated blood in the capillaries of the pulmonary arteries (95 mmHg). As the gases diffuse from a region of higher to a lower concentration, the movement of oxygen is from the alveoli to the blood. The partial pressure of carbon dioxide (pCO2) is higher in deoxygenated blood (45 mmHg) than in alveoli (40 mmHg), therefore carbon dioxide passes from the blood to the alveoli. A diagram of a section of an alveolus with a pulmonary capillary is given below : (Img 108)

Question. What do you mean by respiratory centre? Briefly explain the types of respiratory centre.
Answer.  Respiratory centre is composed of groups of neurons located in the medulla oblongata and pons varolli and regulates respiration. It is of two types : medullary and pons respiratory centres. (i) Medullary respiratory centres are further divided into dorsal and ventral respiratory group. Dorsal respiratory group causes inspiration and ventral respiratory group can either inspiration or expiration. (ii) Pons respiratory centre is divided into pneumotaxic and apneustic centre. Pneumotaxic centre primarily limits the inspiration.

Question. Give the differences between emphysema and occupational respiratory disorder.
Answer. Differences between emphysema and occupational respiratory disorder are as follows:

Question. Why is haemoglobin called conjugated protein? What happens to the molecule at high and low partial pressure of oxygen?
Answer. Haemoglobin is called a conjugated protein as it contains a protein globulin and non-protein heme. Haemoglobin has four polypeptide chains and four heme groups attached to it. It has 4 atoms of iron in ferrous form (Fe2+). So, haemoglobin can react with 4 molecules of oxygen forming oxyhaemoglobin. At high partial pressure of oxygen, haemoglobin combines with oxygen to form oxyhaemoglobin and at low partial pressure of oxygen, the oxyhaemoglobin dissociates into oxygen and haemoglobin.

Question. Explain the mechanism of expiration with the help of diagram.
Answer.  Expiration is the exhalation of foul air out of the lungs. During expiration, the muscles of diaphragm relax, making it a dome-shaped and decreasing the volume of thoracic cavity. The internal intercostal muscles contract, pulling the ribs downward and inward and decreasing the size of thoracic cavity. Contraction of the abdominal muscles compresses the abdominal viscera against the diaphragm, thus resulting in the decrease of the volume of the thoracic cavity. Due to decrease in volume, the intrapulmonary pressure increases. Thus, the air from the cavities of alveoli goes out through the nasal cavities via the alveolar ducts, respiratory bronchioles, bronchioles, bronchi, trachea, larynx, glottis, pharynx, internal nares and external nares. The mechanism of breathing showing expiration can be explained with the help of diagram given below : 

Long Answer Type Questions

Question. (a) Distinguish between breathing and respiration. (b) Describe the olfactory region of the nasal chamber with its function.
Answer. (a) : Differences between breathing and respiration are: (Table 110) 
(b) Olfactory region is the upper region of the nasal chamber that looks yellowish brown. It is lined with a specialised type of pseudostratified columnar epithelium known as olfactory epithelium. The epithelium is confined to the upper part of the nasal chamber and the superior nasal concha. Function : It acts as an organ of smell, as the olfactory epithelium contains sense receptors. It detects the odour of the inspired (inhaled) air. If the odour is pungent, the air is not allowed to pass in.

Question. (a) Describe the exchange of oxygen and carbon dioxide between blood and tissue cells. (b) Diagrammatically explain the external and internal respiration.
Answer. (a) The exchange of gases between tissue, blood capillaries and tissue cells is called internal respiration. In the tissues, exchange of gases occur between the blood and the tissue cells through tissue fluids that surround the tissue cells. Blood that reaches the tissues has more partial pressure of O2 (pO2 = 100 mm of Hg), than that in the body tissue cells (pO2 = 40 mm of Hg). Similarly, partial pressure of CO2 is more in tissues (pCO2 = 45 mm of Hg) than in the blood (pCO2 = 40 mm of Hg). Due to these differences in partial pressure of gases, O2 from blood diffuses in the tissues and CO2 from tissues diffuses into the blood. Gases diffuse from region of higher to lower partial pressure. This exchange of gases occur simultaneously. The venous blood goes to the right side of the heart that sends it to lungs via pulmonary artery for reoxygenation.
(b) Diagrammatic representation of gaseous exchange,
(i) between alveolus and pulmonary blood capillary (external respiration) and (ii) between blood capillary and body tissues cells (internal respiration).