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.

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.

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

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.

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.

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.

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

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.

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).

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.

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

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.

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. 

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.

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.

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.

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.

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

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.

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.

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.

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.