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

First, let's define each term listed in List I and match them with their appropriate descriptions in List II.

List I:

• Expiratory Capacity (EC): This is the maximum volume of air that a person can expel from the lungs after a normal tidal expiration. It is composed of the expiratory reserve volume (ERV) and tidal volume (TV).
• Functional Residual Capacity (FRC): This represents the volume of air present in the lungs at the end of a passive expiration. It is the sum of the residual volume (RV) and the expiratory reserve volume (ERV).
• Vital Capacity (VC): This includes the total volume of air that can be expelled from the lungs after taking as deep an inhalation as possible. Hence, this comprises the tidal volume (TV), inspiratory reserve volume (IRV), and the expiratory reserve volume (ERV).
• Inspiratory Capacity (IC): It refers to the volume of air that can be inhaled after a normal expiration. This combines tidal volume (TV) and inspiratory reserve volume (IRV).

List II:

• I. Expiratory reserve volume + Tidal volume + Inspiratory reserve volume = Vital Capacity (VC).
• II. Tidal volume + Expiratory reserve volume = Expiratory Capacity (EC).
• III. Tidal volume + Inspiratory reserve volume = Inspiratory Capacity (IC).
• IV. Expiratory reserve volume + Residual volume = Functional Residual Capacity (FRC).

Now, let's match the terms:

A (Expiratory Capacity) matches with II.
B (Functional Residual Capacity) matches with IV.
C (Vital Capacity) matches with I.
D (Inspiratory Capacity) matches with III.

The correct option that pairs these correctly is: Option A: A-II, B-IV, C-I, D-III.

The formation of oxyhemoglobin in the alveoli is primarily influenced by the partial pressure of oxygen ( pO₂ ), partial pressure of carbon dioxide ( pCO₂), hydrogen ion concentration ( H⁺ ), and temperature. Understanding these factors will help in selecting the right option that describes the conditions favorable for maximizing the binding of oxygen to hemoglobin in the lungs.
1. Oxygen Partial Pressure ( pO₂ ): High pO 2 enhances the formation of oxyhemoglobin. In the alveoli, where gas exchange occurs, the pO₂ is relatively high, making it a favorable condition for oxyhemoglobin formation as oxygen molecules bind readily to hemoglobin.
2. Carbon Dioxide Partial Pressure ( pCO₂ ): Lower pCO₂ is favorable in the alveoli for oxyhemoglobin formation. High pCO₂ leads to a lower pH (due to formation of carbonic acid), which can cause the release of O₂ from hemoglobin (Bohr effect), reducing hemoglobin's affinity for oxygen.
3. Hydrogen Ion Concentration ( H⁺): Lesser H⁺ concentration, or higher pH, increases the affinity of hemoglobin for oxygen. In alkaline conditions (higher pH), hemoglobin is more likely to bind oxygen, thus forming oxyhemoglobin.
4. Temperature: Temperature also affects oxygen binding. Lower temperatures generally enhance the uptake of oxygen by hemoglobin. However, since the lung environment maintains a stable temperature, significant fluctuations in temperature are less of a consideration in this context compared to pO₂ , pCO₂ , and H⁺ concentration. Given these points, Option B - High pO₂ and Lesser H⁺ concentration - best describes the conditions that are favorable for the formation of oxyhemoglobin in the alveoli. High pO₂ ensures that more oxygen molecules are available to bind with hemoglobin, and a lower H⁺ concentration (higher pH) reduces the release of oxygen from hemoglobin, thereby increasing oxygen uptake.

• The vital capacity (VC) of the lung is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume (IRV), tidal volume (TV), and expiratory reserve volume (ERV).
• Inspiratory reserve volume (IRV) is the amount of air that can be inhaled beyond a normal breath.
• Expiratory reserve volume (ERV) is the amount of air that can be exhaled beyond a normal breath.
• Tidal volume (TV) is the amount of air that is inhaled and exhaled during a normal breath.

Therefore, vital capacity (VC) = IRV + ERV + TV.

• Option (d) is correct because the part starting with the external nostrils upto the terminal bronchioles constitute the conducting part; whereas the alveoli and their ducts form the respiratory or exchange part of the respiratory system.
• The conducting part transports the atmospheric air to the alveoli, clears it from foreign particles, humidifies and also bring the air to body temperature. Exchange part is the site of actual diffusion of O₂/CO₂ between blood and atmospheric air.

• Option (b) is the correct answer because every 100 ml of oxygenated blood can deliver around 5 ml of O₂ to the tissues under normal physiological conditions.
• Option (c), (d) and (a) are incorrect because every 100 ml of deoxygenated blood delivers approximately 4 ml of CO₂ to the alveoli.

Option (d) is the correct answer because statements (a), (c) and (e) are correct.

• Vital capacity includes ERV, TV and IRV.
• Vital capacity is the maximum volume of air a person can breathe in after a forced expiration or the maximum volume of air a person can breathe out after a forced inspiration.
• Statement (b) is incorrect as total volume of air a person can inspire after a normal expiration is termed as inspiratory capacity (IC).
• Statement (d) is incorrect as ERV, RV, IRV and TV comprise total lung capacity.

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."

Reduction of pH of blood will decrease the affinity of hemoglobin with oxygen which in turn causes acidosis.

Intrapleural pressure is the pressure of air within the pleural cavity. Intrapleural pressure is always negative, which acts like a suction to keep the lungs inflated and prevent them from collapsing. The negative intrapleural pressure is due to three main factors: surface tension of the alveolar fluid; elasticity of lungs; elasticity of thoracic wall. Normally, there is a difference between intrapleural and intrapulmonary pressure, which is called transpulmonary pressure. This transpulmonary pressure creates the suction to keep the lungs inflated. If there is no pressure difference, there is no suction and lungs will collapse.

Emphysema results when the delicate linings of the air sacs in the lungs become damaged beyond repair. Most commonly, the toxins in cigarette smoke create the damage. Emphysema is called smoker’s disease.

Asthma is an allergic condition in which the tissue surrounding the bronchioles of the lungs swell up and compress the bronchioles thus causing difficulty in breathing. This allergy mainly involves IgE antibodies and chemicals like histamine and serotonin from the mast cells.

The partial pressure of oxygen in alveolar air is 104mmHg whereas it is 40mmHg in deoxygenated blood and 95mmHg in oxygenated blood.

Excess CO₂ mainly stimulates the respiratory centre of the brain and increases the inspiratory and expiratory signals to the respiratory muscles. O₂ does not have a significant direct effect on the respiratory centre of the brain in controlling respiration. 

• About 70% of CO₂ (about 2.5ml per 100 ml. of blood), received by blood from the tissues, enters the RBCs where it reacts with water to form carbonic acid (H₂CO₃). 
• Carbonic anhydrase, exclusively found in RBCs, speeds up the formation of H₂CO₃ and rapidly converts it back to carbon dioxide and water when blood reaches the lungs. Almost as rapidly as formed, all carbonic acid of RBCs dissociates into hydrogen (H⁺) and bicarbonate ions (HCO^-₃). 

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.

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."

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."

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

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

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 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.

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