31 Years NEET Previous Year Questions: Breathing & Exchange of Gases - NEET MCQ

In the alveoli, where there is high pO₂, low pCO₂, lesser H⁺ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, whereas in the tissues, where low pO₂, high pCO₂, high H⁺ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin.

Line in NCERT: "In the alveoli, where there is high pO2, low pCO2, lesser H+ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin."

Inspiration is initiated by contraction of diaphragm which increases volume of thoracic chamber in antero-posterior axis and contraction of external inter –costal muscles which lifts up the ribs and sternum causing increases in volume of thoracic chamber in dorsoventral axis.

Line in NCERT: "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 overall increase in the thoracic volume causes a similar increase in pulmonary volume."

Expiratory capacity is the total volume of air a person can expire after normal inspiration. It includes tidal volume and expiratory reserve volume.
EC = TV + ERV = 500 + 1000 = 1500 mL

Line in NCERT: "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)."

Asthma is a difficulty in breathing, causing wheezing due to inflammation of bronchi and bronchioles. 

Emphysema is a chronic disorder in which abnormal distension of the bronchioles or alveolar sacs of the lungs occurs due to which respiratory surface is decreased for the exchange of oxygen and carbon dioxide.

Line in NCERT: "Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles. Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased."

Residual volume is the volume of air which remains in the lungs after the most forceful expiration. This residual air enables the lungs to continue exchange of gases even after maximum exhalation. Due to this, lungs do not collapse even after forceful expiration.

Line in NCERT: "Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration."

Frog has lungs as its main respiratory organs but during hibernation & aestivation and during its habitat in water it respires through skin

The very thin alveolar wall (about 0.0001 mm) is composed of moist, nonciliated, squamous epithelial cells.

Line in NCERT: "the thin squamous epithelium of alveoli"

CO₂ from the respiratory tissues to the lungs is transported by the blood in 3 ways :

(i) In dissolved state or as a physical solution : Very small amount physically dissolved in plasma (7% i.e. @ 0.3 ml of CO₂ by each 100 ml of blood)

(ii) Bicarbonate ions : @ 70% (i.e. @ 2.5 ml per 100 ml of blood) CO₂ diffuses in plasma & then into RBCs where it (in the  presence of carbonic anhydrase) combines with H₂O to form carbonic acid which is almost spontaneously dissociated into hydrogen ion & bicarbonate ions.

(iii) Carbaminohaemoglobin : @ 23% (i.e. @ 1 ml of CO₂ per 100 ml of blood) combines with haemoglobin forming an unstable compound

Line in NCERT: "Nearly 20-25 per cent of CO2 is transported by RBCs whereas 70 per cent of it is carried as bicarbonate. About 7 per cent of CO2 is carried in a dissolved state through plasma."

It is the relationship between the percentage saturation of haemoglobin (by volume) in the blood and the oxygen tension (in partial tension) PO₂ of the blood.
It is usually a sigmoid plot. Haemoglobin molecules can bind up to four oxygen molecules in a reversible way. The shape of the curve results from the interaction of bound oxygen molecules with incoming molecules. The binding of the first molecule is difficult. However, this facilitates the binding of the second and third molecules, and it is only when the fourth molecule is to be bound that the difficulty increases, partly as a result of crowding of the haemoglobin molecule, partly as a natural tendency of oxygen to dissociate.

The O₂-Hb dissociation curve is a sigmoidal curve that represents the relationship between O₂ concentration and the percentage saturation of Hb. As the concentration increases from about 90% there is a significant plateau in the curve, which has several important biological repercussions.

Line in NCERT: "A sigmoid curve is obtained when percentage saturation of haemoglobin with O2 is plotted against the pO2."

The pathway of inhaled air is - Nostrils - pharynx (common passage for food & air) - larynx (voice box) - trachea (the wind pipe) - bronchi (2 for each side lungs) - bronchioles (give arise to alveolar ducts) - alveoli (the exchange site for gases in the form of small sacs or pouches).

Line in NCERT: "It leads to a nasal chamber through the nasal passage. The nasal chamber opens into the pharynx, a portion of which is the common passage for food and air. The pharynx opens through the larynx region into the trachea."

CO₂ enters RBC and reacts with water to form carbonic acid. Carbonic acid dissociates to form bicarbonate and hydrogen ions. Some bicarbonate ions are transported in erythrocytes while some diffuse into the blood plasma. Exit of bicarbonate ions change the ionic balance between the plasma and erythrocytes. To restore this balance chloride ions diffuse from plasma into erythrocytes. Due to this the pH of blood is maintained.

Line in NCERT: "Nearly 70 per cent of carbon dioxide is transported as bicarbonate (HCO3) with the help of the enzyme carbonic anhydrase."

Carbon dioxide is transported via blood to lungs mostly as carbaminohaemoglobin and carbonic acid. It is released in lungs in exchange with oxygen.

Line in NCERT: "20-25 per cent of carbon dioxide is carried by haemoglobin as carbamino-haemoglobin."

At the altitude of 5400 meters the low atmospheric pressure of O₂ will be too low so the solubility of oxygen in the blood will be very less hence the oxygen carried by each RBC will be too less. But to fulfill the oxygen requirement of the body blood has to carry more oxygen to the body tissue and this is done by the increased no. of RBCs.

The total volume of air that can be expelled from the lungs after maximum inspiration and then expiring to the maximum is known as the vital capacity. The volume of air that remains inside lungs at the end of maximum forceful expiration is the residual volume. Expiratory reserve volume is the maximum extra volume of air that can be expired by forceful expiration after a normal tidal expiration. Total lung capacity is the maximum volume of air that can be contained in the lungs after maximum inspiration.

Line in NCERT: "Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration. This averages 1100 mL to 1200 mL."

Alveoli are the site of the respiratory exchange of gases. Oxygen from the  alveolar air diffuses through the alveolar epithelium and the capillary endothelium into the capillary blood and carbon dioxide diffuses in the opposite direction. 

Line in NCERT: "The diffusion membrane is made up of three major layers namely, the thin squamous epithelium of alveoli, the endothelium of alveolar capillaries and the basement substance (composed of a thin basement membrane supporting the squamous epithelium and the basement membrane surrounding the single layer endothelial cells of capillaries) in between them."

Gaseous exchange between blood (dissolved phase) and alveolar air (gaseous phase) across respiratory membrane occurs by simple diffusion. Obviously, it depends upon the concentration gradient (=partial pressure) of the concerned gases in blood and alveolar air.

Line in NCERT: "Exchange of O2 and CO2 at the alveoli and tissues occur by diffusion."

During the transport of CO₂ through the blood, bicarbonate ions diffuse out of RBCs while chloride ions from plasma enter the RBCs to maintain ionic equilibrium. This is called chloride shift.

Brain is the most vital organ. It stops functioning in the absence of  O₂.

The breathing becomes faster and deeper in order to oxygenate the blood at a fast rate. Shallow and slow breathing occurs during rest.

Line in NCERT: "A chemosensitive area is situated adjacent to the rhythm centre which is highly sensitive to CO2 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."

Carboxyhaemoglobin is the stable product formed by the association of CO and Hb in the blood. The association of carbon dioxide and haemoglobin forms carbamino haemoglobin.

Since RBCS do not have mitochondria so they can respire only anaerobically.

Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. Theintercostal muscles are mainly involved in the mechanical aspect of breathing. These muscles help expand and shrink the size of the chest cavity to facilitate breathing.Inter-coastal muscles occur in the ribs.

Line in NCERT: "The diaphragm and a specialised set of muscles - external and internal intercostals between the ribs, help in generation of such gradients."

Vital capacity of lungs is largest possible expiration after largest possible inspiration that is greatest. Volume of air can be exchanged in single respiration or amount of air breath in and out with greatest  possible efforts.
VC = TRV +TV + ERV 
      = 3000 + 500 + 1100 
      = 4600 ml.

Line in NCERT: "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."

Respiratory Capacities:
- i) Inspiratory Capacity (IC): The maximum volume of air that can be inhaled after a normal expiration.
- ii) Functional Residual Capacity (FRC): The volume of air remaining in the lungs after a normal expiration.
- iii) Vital Capacity (VC): The maximum volume of air that can be exhaled after a maximum inhalation.
- iv) Total Lung Capacity (TLC): The total volume of air that the lungs can hold.

Respiratory Volumes:
- 1200mL: This volume doesn't match any of the capacities given.
- 2500mL: This volume matches with FRC (Functional Residual Capacity).
- 3500mL: This volume doesn't match any of the capacities given.
- 4500mL: This volume matches with IC (Inspiratory Capacity).

Therefore, the correct matching of two capacities and volumes is:
- Functional Residual Capacity (FRC): 2500mL
- Inspiratory Capacity (IC): 4500mL

So, the correct answer is option C: (iv) 3500 mL, (i) 1200mL0mL Inspiratory volume 3500mL

Line in NCERT: "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." "Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration. This averages 1100 mL to 1200 mL." "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 (TLC): 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."

At high altitude, the body undergoes numerous changes in order to increase oxygen delivery to cells and improve the efficiency of oxygen usage. The early changes include increased breathing rate and increased red blood cell production

The process of breathing involves the pathway of the human respiratory system and includes the nasal cavities, oral cavities, pharynx, trachea, primary bronchi, secondary bronchi  and lungs with  bronchioles and alveoli present. Breathing is a 2-fold process which includes breathing in and breathing out. During this process, the diaphragm which is the dome-shaped sheet of muscle located below the lungs contracts and expands along with the intercostal muscles to force air in and out of the lungs. Since intercostal muscles are also involved in the process of respiration, deeper respiration results in the movement of ribs too. Hence most of us can consciously breathe in and breathe out by moving the diaphragm alone.

Line in NCERT: "B: One can consciously breathe in and breathe out by moving the diaphragm alone, without moving the ribs at all."

Correct Answer :- c

Explanation : Cigarette smoking causes an immunogenic response. It results in increased levels of inflammatory markers. It may result in the development of irreversible narrowing of bronchial tubes due to inflammation and scarring. It causes cancer, chronic lung disease. The pneumotaxic center in the pons region of the brainstem moderate the functions of the respiratory rhythm centre. It reduces the duration of inspiration and therefore alters the respiratory rate. Workers in grinding and stone-breaking industries may suffer from lung fibrosis. Exposure to environmental pollutants like silica, metal dusts, bacteria and animal proteins can lead to lung fibrosis. Carbon dioxide is carried in blood as bicarbonate, dissolved CO2 and carbaminohemoglobin. About 29% of it is carried as carbaminohemoglobin.

Line in NCERT: "Workers in such industries should wear protective masks."

Alveoli are very thin, irregular walled bag like structures for gaseous exchange. Tracheae bronchi and bronchioles are supported by incomplete cartilaginous rings. Double layered pleural membrane surrounds the lungs with pleural fluid between them. It reduces friction on the lung surface.

Line in NCERT: "Each terminal bronchiole gives rise to a number of very thin, irregular-walled and vascularised bag-like structures called alveoli."

A is Pulmonary vein which takes pure blood from lungs to heart. B is dorsal aorta  which takes pure blood from heart to various body parts. C is Vena cava which takes impure blood from various body pars to right auricle of heart. D is pulmonary artery which takes impure blood from heart to lungs.

The number of spiracles in cockroach is 10-pairs (2-pairs in thoracic and 8-pairs in abdominal region).  The thoracic pairs of spiracles are present on pleuron between prothorax - mesothorax and metathorax. Each spiracle opens into a chamber called atrium.  After atrium the tracheal tube ramifies into fine branches of tracheae, and then tracheoles.