Respiration – Transport of Gases and Regulation of Respiration: NEET MCQs with Answers

15 free questions on Respiration – Transport of Gases and Regulation of Respiration for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Transport of Gases and Regulation of Respiration

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Question 1

Previous-year question
Assertion: During transport of gases, about 20–25 percent of CO₂ is carried by haemoglobin as carbamino-haemoglobin. [Re-NEET 2024]
Reason: This binding is related to high pCO₂ and low pO₂ in the tissues.
  1. A is true but R is false.
  2. A is false but R is true.
  3. Both A and R are true and R is the correct explanation of A.
  4. Both A and R are true but R is NOT the correct explanation of A.
Show answer
Answer: (C) Both A and R are true and R is the correct explanation of A.
Explanation: About 20–25 percent of CO₂ is carried by haemoglobin as carbamino-haemoglobin, so A is true. This binding depends on partial pressure of CO₂ (and of O₂): in tissues, where pCO₂ is high and pO₂ low, more CO₂ binds; in alveoli the reverse causes its release. Hence R is true and correctly explains A.

Question 2

Previous-year question
In the regulation of breathing, a chemosensitive area located next to the rhythm centre in the medulla of the brain is highly sensitive to: [NEET (Overseas) 2022]
  1. CO₂
  2. O₂
  3. N₂
  4. HCO₃⁻
Show answer
Answer: (A) CO₂
Explanation: The chemosensitive area adjacent to the respiratory rhythm centre is highly sensitive to CO₂ and H⁺ ions; an increase in these activates the rhythm centre to adjust breathing. The role of O₂ in regulating the respiratory rhythm is quite insignificant, and N₂ and HCO₃⁻ do not act on this area.

Question 3

Previous-year question
The respiratory centres which control inspiration and expiration are located in the [AIPMT 1989]
  1. diencephalon
  2. medulla oblongata
  3. cerebellum
  4. spinal cord
Show answer
Answer: (B) medulla oblongata
Explanation: The respiratory rhythm centre lies in the medulla oblongata. Its dorsal group of neurons regulates inspiration, while the ventral group regulates both inspiration and expiration. A pneumotaxic centre in the pons can moderate the function of this centre.

Question 4

Previous-year question
When you hold your breath, which of the following gas changes in blood would first lead to the urge to breathe? [AIPMT 1990]
  1. Falling CO₂ concentration
  2. Rising CO₂ and falling O₂ concentration
  3. Falling O₂ concentration
  4. Rising CO₂ concentration
Show answer
Answer: (D) Rising CO₂ concentration
Explanation: Holding the breath causes CO₂ to accumulate, making the blood more acidic. This change in pH triggers the chemosensitive receptors that activate the respiratory centre of the brain, producing the urge to release the breath. It is the rise in CO₂, not the fall in O₂, that is the primary stimulus.

Question 5

Previous-year question
Carbonic anhydrase occurs in [AIPMT 1991]
  1. lymphocytes
  2. blood plasma
  3. RBC
  4. leucocytes
Show answer
Answer: (C) RBC
Explanation: The erythrocyte contains a high concentration of carbonic anhydrase, the enzyme that catalyses the reversible reaction between CO₂ and H₂O. This greatly accelerates the transport of CO₂ from the tissues to the lungs.

Question 6

Previous-year question
Carbon dioxide is transported from the tissues to the respiratory surface by only [AIPMT 1993]
  1. plasma and erythrocytes
  2. plasma
  3. erythrocytes
  4. erythrocytes and leucocytes
Show answer
Answer: (A) plasma and erythrocytes
Explanation: CO₂ is carried by the plasma and the erythrocytes: about 70% as bicarbonate in the plasma, 23% as carbaminohaemoglobin within the RBCs, and 7% dissolved in the plasma. Its transport is easier than that of oxygen because of its high solubility in water.

Question 7

Previous-year question
The oxygen dissociation curve of haemoglobin is [AIPMT 1994]
  1. sigmoid
  2. hyperbolic
  3. linear
  4. hypobolic
Show answer
Answer: (A) sigmoid
Explanation: The curve obtained by plotting the percentage saturation of haemoglobin against oxygen tension at 38 °C and pH 7.4 is sigmoid (S-shaped). Dissociation of oxyhaemoglobin is promoted by a rise in body temperature and by low pH (high CO₂).
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Question 8

Previous-year question
Although much CO₂ is carried in the blood, the blood does not become acidic, because [AIPMT 1995]
  1. it is absorbed by the leucocytes
  2. blood buffers play an important role in CO₂ transport
  3. it combines with water to form H₂CO₃ which is neutralised by Na₂CO₃
  4. it is continuously diffused through tissues and is not allowed to accumulate
Show answer
Answer: (B) blood buffers play an important role in CO₂ transport
Explanation: Sodium bicarbonate is the chief buffer of the blood and plays a central role in CO₂ transport. Carbonic acid dissociates into H⁺ and HCO₃⁻, and the bicarbonate combines with sodium to form sodium bicarbonate, so the concentration of free carbonic acid — and hence the acidity of the blood — does not rise.

Question 9

Previous-year question
Carbon dioxide is transported via blood to the lungs as [AIPMT 1995]
  1. dissolved in blood plasma
  2. in the form of carbonic acid only
  3. in combination with haemoglobin only
  4. carbaminohaemoglobin and as carbonic acid
Show answer
Answer: (D) carbaminohaemoglobin and as carbonic acid
Explanation: Most of the CO₂ (about 70%) dissolves in the plasma and reacts with water to form carbonic acid, a reaction accelerated inside the RBCs by carbonic anhydrase. A further 23% or so binds loosely to haemoglobin to form the unstable compound carbaminohaemoglobin.

Question 10

Previous-year question
At high altitude, the RBCs in the human blood will [AIPMT 1995]
  1. increase in size
  2. decrease in size
  3. increase in number
  4. decrease in number
Show answer
Answer: (C) increase in number
Explanation: At high altitude the low oxygen concentration triggers erythropoietin secretion, and the number of RBCs increases so that an adequate oxygen supply can still be maintained to the organs.

Question 11

Previous-year question
Which one of the following statements about blood constituents and the transport of respiratory gases is most accurate? [AIPMT 1996]
  1. RBCs transport oxygen whereas WBCs transport CO₂
  2. RBCs transport oxygen whereas plasma transports only CO₂
  3. RBCs as well as WBCs transport both oxygen and CO₂
  4. RBCs as well as plasma transport both oxygen and CO₂
Show answer
Answer: (D) RBCs as well as plasma transport both oxygen and CO₂
Explanation: Both RBCs and plasma carry oxygen and carbon dioxide, either chemically bound or in the dissolved state. Around 97% of O₂ travels with the RBCs and 3% dissolved in the plasma, while CO₂ is carried about 70% as plasma bicarbonate, 23% as carbamino-haemoglobin and 7% dissolved. WBCs play no role in gas transport.

Question 12

Previous-year question
In the alveoli of the lungs, the air at the site of gas exchange is separated from the blood by [AIPMT 1997]
  1. alveolar epithelium only
  2. alveolar epithelium and capillary endothelium
  3. alveolar epithelium, capillary endothelium and tunica adventitia
  4. alveolar epithelium, capillary endothelium, a thin layer of tunica media and tunica adventitia
Show answer
Answer: (B) alveolar epithelium and capillary endothelium
Explanation: The wall of the pulmonary capillaries consists only of the tunica interna, which is made of simple squamous endothelium, and the alveolar wall is likewise a very thin squamous epithelium. Only these two extremely thin layers separate air from blood.

Question 13

Previous-year question
The process of migration of chloride ions from plasma to RBC and of carbonate ions from RBC to plasma is [AIPMT 1999]
  1. chloride shift
  2. ionic shift
  3. atomic shift
  4. Na⁺ pump
Show answer
Answer: (A) chloride shift
Explanation: To maintain the electrostatic neutrality of the plasma, chloride ions diffuse from the plasma into the RBCs as bicarbonate ions move out. This phenomenon is called the chloride shift or Hamburger shift, and it raises the chloride content of RBCs in deoxygenated blood.

Question 14

Previous-year question
When the CO₂ concentration in the blood increases, breathing becomes [AIPMT 2004]
  1. shallower and slow
  2. unaffected
  3. slow and deep
  4. faster and deeper
Show answer
Answer: (D) faster and deeper
Explanation: A rise in CO₂ concentration stimulates the chemosensitive area associated with the respiratory rhythm centre, making breathing faster and deeper. By the Bohr effect, the increased CO₂ also lowers haemoglobin's affinity for oxygen, so oxygen delivery to the respiring tissues is accelerated.

Question 15

Previous-year 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? [AIPMT 2004]
  1. The patient has been inhaling polluted air containing an unusually high content of carbon disulphide
  2. The patient has been inhaling polluted air containing an unusually high content of chloroform
  3. The patient has been inhaling polluted air containing an unusually high content of carbon dioxide
  4. The patient has been inhaling polluted air containing an unusually high content of carbon monoxide
Show answer
Answer: (D) The patient has been inhaling polluted air containing an unusually high content of carbon monoxide
Explanation: Carbon monoxide forms a stable compound with haemoglobin called carboxyhaemoglobin. Since the affinity of haemoglobin for CO is about 210 times greater than for O₂, even small amounts block oxygen transport and can cause death by hypoxia: Haemoglobin + CO ⇌ Carboxyhaemoglobin

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