Test: Exchange & Transport of Gases-1 - NEET MCQ

Trachea divides at the level of 5th thoracic vertebra into a right and left primary bronchi.

Line in NCERT: "Trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of 5th thoracic vertebra into a right and left primary bronchi."

Vital capacity includes ERV, TV and IRV or the maximum volume of air a person can breathe out after a forced inspiration.

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."

• 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.
• This clearly indicates that oxygen gets bound to haemoglobin in the lung surface and gets dissociated at the tissues. 

Line in NCERT: "where low pO2, high pCO2, high H* concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin."

20 – 25% of CO₂ is transported to the alveoli as carbamino-haemoglobin.

Line in NCERT: "Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO2 to the alveoli." "About 20-25 per cent of CO2 is transported by RBCs whereas 70 per cent of it is carried as bicarbonate." "RBCs contain a very high concentration of the enzyme, carbonic anhydrase and minute quantities of the same is present in the plasma too."

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: "where low pO2, high pCO2, high H+ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin."

Epiglottis to prevent the entry of food into the larynx.

Line in NCERT: "During swallowing glottis can be covered by a thin elastic cartilaginous flap called epiglottis to prevent the entry of food into the larynx."

The solubility of carbon dioxide is 20-25 times higher than that of oxygen, the amount of carbon dioxide that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of oxygen.

Line in NCERT: "As the solubility of CO2 is 20-25 times higher than that of O2, the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of O2."

• Statement i is correct because it describes the basic function of breathing, which includes taking in oxygen from the atmosphere and expelling carbon dioxide from the alveoli.
• Statement ii is also correct as it highlights the diffusion of gases (O2 and CO2) across the alveolar membrane, which is a critical step in the respiratory process.
• Statement iii is incorrect because blood transports both oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs.
• Statement iv is incorrect because cells utilize oxygen primarily for catabolic reactions (energy production), which results in the release of carbon dioxide, not for anabolic reactions.

Therefore, the correct statements are i and ii, making Option D (i, ii, and iv) the right answer.

Line in NCERT: "Respiration involves the following steps: (i) Breathing or pulmonary ventilation by which atmospheric air is drawn in and CO2 rich alveolar air is released out. (ii) Diffusion of gases (O2 and CO2) across alveolar membrane."

To determine the correct statements, let's analyze each:

- Statement i is correct as it accurately describes the composition of the diffusion membrane, which includes the thin squamous epithelium of alveoli, the endothelium of capillaries, and the basement substance.

- Statement ii is incorrect. The total thickness of the diffusion membrane is much less than a millimeter, which contradicts the statement.

- Statement iii is correct because it aligns with the physiological principle that the conditions in the body promote the diffusion of oxygen (O2) from the alveoli to the tissues.

- Statement iv is incorrect as it misrepresents the diffusion process; CO2 diffuses through a similarly thin membrane, not a thicker one.

Thus, the correct answer is Option A: i and iii.

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."

- The Assertion is true: Approximately 97 percent of oxygen is indeed transported by RBCs, which contain hemoglobin that binds oxygen effectively.

- The Reason is also true: A significant portion of carbon dioxide (about 70 percent) is carried in the blood as bicarbonate ions, which is a critical aspect of carbon dioxide transport.

- However, the Reason does not explain the Assertion directly. The transport mechanisms for oxygen and carbon dioxide are distinct, and one does not clarify the other. Thus, the correct answer is Option B.

Line in NCERT: "About 97 per cent of O2 is transported by RBCs in the blood. The remaining 3 per cent of O2 is carried in a dissolved state through the plasma. Nearly 20-25 per cent of CO2 is transported by RBCs whereas 70 per cent of it is carried as bicarbonate."

Wheezing is a common symptom of asthma, characterized by a high-pitched whistling sound during breathing.

Line in NCERT: "Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles."

- Statement i is correct because the respiratory rhythm centre is indeed located in the medulla region of the brain, which is responsible for the basic rhythm of breathing.

- Statement ii is incorrect; the pneumotaxic centre moderates the functions of the respiratory rhythm centre by reducing the duration of inspiration, not enhancing it.

- Statement iii is correct as the chemosensitive area near the rhythm centre responds to elevated levels of CO2 and hydrogen ions, leading to adjustments in the respiratory process.

- Statement iv is incorrect; the text states that the role of oxygen in regulating respiratory rhythm is quite insignificant.

Thus, the correct statements are i and iii, making Option A the right answer.

Line in NCERT: "Respiratory rhythm is maintained by the respiratory centre in the medulla region of brain. A pneumotaxic centre in the pons region of the brain and a chemosensitive area in the medulla can alter respiratory mechanism."

- Statement i is correct: Tidal Volume (TV) is indeed approximately 500 mL and represents the volume of air exchanged during normal breathing.

- Statement ii is incorrect: Residual Volume (RV) is the volume of air that remains in the lungs after a forcible expiration, not the volume that can be forcibly expired.

- Statement iii is correct: Vital Capacity (VC) is the maximum volume of air a person can breathe out after a forced inspiration and does include TV, IRV, and ERV.

- Statement iv is incorrect: Functional Residual Capacity (FRC) is the volume of air remaining in the lungs after a normal expiration and includes ERV and RV, not the volume after maximum inspiration.

Thus, the correct statements are i and iii, leading to the correct answer being Option A.

Line in NCERT: "Tidal Volume (TV): Volume of air inspired or expired during a normal respiration. It is approx. 500 mL." "Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration." "Vital Capacity (VC): The maximum volume of air a person can breathe in after a forced expiration. This includes ERV, TV and IRV." "Functional Residual Capacity (FRC): Volume of air that will remain in the lungs after a normal expiration."

• Assertion (A) is true because alveoli are indeed the primary sites for gas exchange in the respiratory system, facilitating the transfer of oxygen into the blood and the removal of carbon dioxide.
• Reason (R) is also true; the thickness of the alveolar membrane affects diffusion rates, with thinner membranes generally allowing for more efficient gas exchange.
• Furthermore, the reason correctly explains the assertion, as a thinner alveolar membrane enhances the efficiency of gas exchange, thereby supporting the assertion about the role of alveoli.

Line in NCERT: "Rate of diffusion is dependent on the partial pressure gradients of O2 (pO2) and CO2 (pCO2), their solubility as well as the thickness of the diffusion surface."

The sternum forms the ventral boundary of the thoracic chamber, providing structural support and protection for the organs within.

Line in NCERT: "The thoracic chamber is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs and on the lower side by the dome-shaped diaphragm."