Transport of gases MCQs With Answer

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Transport of gases MCQs With Answer is an essential review for B. Pharm students preparing for exams in respiratory physiology and clinical pharmacology. This concise, Student-friendly guide covers oxygen and carbon dioxide transport, hemoglobin function, the oxygen-hemoglobin dissociation curve, partial pressures, 2,3-BPG, Bohr and Haldane effects, and clinically relevant disorders like methemoglobinemia and CO poisoning. Each MCQ is designed to deepen understanding of physiological principles, gas exchange equations, and drug effects that alter gas transport. Practicing these questions will strengthen your problem-solving skills and clinical reasoning for pharmacy practice. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which form carries the majority of carbon dioxide in venous blood?

  • Plasma dissolved CO2
  • Carbamino compounds bound to hemoglobin
  • Bicarbonate (HCO3−)
  • CO2 bound to plasma proteins

Correct Answer: Bicarbonate (HCO3−)

Q2. Which equation expresses the oxygen content (CaO2) of arterial blood?

  • CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2)
  • CaO2 = (Hb × 0.003 × SaO2) + (1.34 × PaO2)
  • CaO2 = (PaO2 × 1.34) + (Hb × 0.003 × SaO2)
  • CaO2 = (Hb × PaO2) + (1.34 × SaO2)

Correct Answer: CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2)

Q3. A rightward shift of the oxygen-hemoglobin dissociation curve indicates:

  • Increased Hb affinity for O2
  • Decreased O2 unloading to tissues
  • Increased O2 unloading to tissues
  • No change in oxygen delivery

Correct Answer: Increased O2 unloading to tissues

Q4. Which factor does NOT cause a right shift of the oxyhemoglobin dissociation curve?

  • Increased temperature
  • Increased 2,3-BPG
  • Decreased pH (acidosis)
  • Fetal hemoglobin (HbF)

Correct Answer: Fetal hemoglobin (HbF)

Q5. The Bohr effect describes how:

  • CO2 increases hemoglobin’s affinity for O2
  • Decreased pH shifts the O2 curve left
  • Increased CO2 and H+ reduce O2 affinity of hemoglobin
  • 2,3-BPG increases O2 affinity of hemoglobin

Correct Answer: Increased CO2 and H+ reduce O2 affinity of hemoglobin

Q6. The Haldane effect refers to:

  • Oxygenation of blood decreases CO2 carrying capacity of hemoglobin
  • Oxygenation increases hemoglobin’s capacity to carry CO2
  • Temperature effects on CO2 solubility
  • Effect of 2,3-BPG on CO2 transport

Correct Answer: Oxygenation of blood decreases CO2 carrying capacity of hemoglobin

Q7. Which enzyme catalyzes the rapid conversion of CO2 and H2O to HCO3− and H+ in erythrocytes?

  • Carbonic anhydrase
  • Carbamoyl phosphate synthetase
  • Phosphofructokinase
  • Carbonyl reductase

Correct Answer: Carbonic anhydrase

Q8. 2,3-Bisphosphoglycerate (2,3-BPG) in red blood cells primarily:

  • Increases hemoglobin’s O2 affinity
  • Decreases hemoglobin’s O2 affinity
  • Converts O2 to O3
  • Inactivates carbonic anhydrase

Correct Answer: Decreases hemoglobin’s O2 affinity

Q9. Which of the following increases 2,3-BPG levels?

  • Acute hyperventilation
  • Chronic hypoxia (e.g., high altitude)
  • Hypothyroidism
  • Carbon monoxide exposure

Correct Answer: Chronic hypoxia (e.g., high altitude)

Q10. Carboxyhemoglobin is formed when hemoglobin binds:

  • Oxygen
  • Carbon dioxide
  • Carbon monoxide
  • Nitric oxide

Correct Answer: Carbon monoxide

Q11. Which statement about carbon monoxide (CO) poisoning is true?

  • CO decreases hemoglobin’s affinity for O2
  • Pulse oximetry reliably detects CO poisoning
  • CO binds to hemoglobin with much higher affinity than O2
  • CO primarily increases PaO2

Correct Answer: CO binds to hemoglobin with much higher affinity than O2

Q12. Methemoglobinemia results from oxidation of the ferrous iron (Fe2+) in hemoglobin to:

  • Fe0
  • Fe3+
  • Fe4+
  • Fe1+

Correct Answer: Fe3+

Q13. Which drug is commonly associated with causing methemoglobinemia?

  • Nitroglycerin
  • Dapsone
  • Amoxicillin
  • Acetaminophen

Correct Answer: Dapsone

Q14. The main site of gas exchange in the lung is:

  • Bronchi
  • Alveolar sacs (respiratory zone)
  • Trachea
  • Terminal bronchioles only

Correct Answer: Alveolar sacs (respiratory zone)

Q15. Fick’s law of diffusion states that gas transfer across a membrane is directly proportional to:

  • Membrane thickness
  • Surface area and partial pressure difference
  • Molecular weight squared
  • Length of the airways

Correct Answer: Surface area and partial pressure difference

Q16. Henry’s law is most relevant to gas transport because it relates:

  • Diffusion coefficient to membrane thickness
  • Gas solubility in liquid to its partial pressure above the liquid
  • Hemoglobin saturation to pH
  • 2,3-BPG concentration to oxygen affinity

Correct Answer: Gas solubility in liquid to its partial pressure above the liquid

Q17. Which gas is more soluble in plasma per mmHg of partial pressure, CO2 or O2?

  • O2 is more soluble
  • CO2 is more soluble
  • They have equal solubility
  • Neither is soluble

Correct Answer: CO2 is more soluble

Q18. At standard physiological conditions, the majority of oxygen in arterial blood is transported as:

  • Dissolved O2 in plasma
  • O2 chemically bound to hemoglobin
  • O2 bound to plasma proteins
  • O2 as bicarbonate

Correct Answer: O2 chemically bound to hemoglobin

Q19. Which measurement indicates oxygenation of arterial blood directly?

  • SaO2 (arterial O2 saturation)
  • Hb concentration
  • HCO3− concentration
  • PaCO2

Correct Answer: SaO2 (arterial O2 saturation)

Q20. The alveolar gas equation estimates alveolar O2 (PAO2). Which variable is included in the equation?

  • Inspired O2 fraction (FiO2)
  • Hemoglobin concentration
  • 2,3-BPG concentration
  • Pulse oximeter reading

Correct Answer: Inspired O2 fraction (FiO2)

Q21. Which condition would SHIFT the oxyhemoglobin dissociation curve to the LEFT?

  • Increased temperature
  • Increased 2,3-BPG
  • Decreased pH (acidosis)
  • Presence of fetal hemoglobin (HbF)

Correct Answer: Presence of fetal hemoglobin (HbF)

Q22. Which statement about fetal hemoglobin (HbF) is correct?

  • HbF has a lower affinity for O2 than adult HbA
  • HbF binds 2,3-BPG more tightly than HbA
  • HbF has a higher affinity for O2 promoting O2 transfer across the placenta
  • HbF causes a right shift of the O2 dissociation curve

Correct Answer: HbF has a higher affinity for O2 promoting O2 transfer across the placenta

Q23. Which of the following best describes carbaminohemoglobin formation?

  • CO2 binds to the heme iron
  • CO2 binds to amino groups of globin chains
  • CO2 is converted to bicarbonate only
  • CO2 is stored as carbonic acid in plasma

Correct Answer: CO2 binds to amino groups of globin chains

Q24. A patient has a PaO2 of 60 mmHg. The approximate arterial O2 saturation (SaO2) is closest to:

  • 99%
  • 97%
  • 90%
  • 75%

Correct Answer: 90%

Q25. Which physiologic change increases oxygen delivery to tissues despite unchanged arterial PO2?

  • Decrease in cardiac output
  • Decrease in hemoglobin concentration
  • Increase in hemoglobin concentration
  • Decrease in PaCO2

Correct Answer: Increase in hemoglobin concentration

Q26. Which clinical measurement is least affected by carbon monoxide poisoning?

  • Pulse oximeter reading
  • Measured PaO2 on arterial blood gas
  • Carboxyhemoglobin level
  • Calculated O2 content

Correct Answer: Measured PaO2 on arterial blood gas

Q27. Which of the following decreases arterial oxygen content (CaO2) the most?

  • Mild hypoxemia (PaO2 from 100 to 80 mmHg)
  • Moderate anemia (drop in Hb from 15 to 8 g/dL)
  • Slight hyperventilation
  • Slight increase in PaO2 (100 to 120 mmHg)

Correct Answer: Moderate anemia (drop in Hb from 15 to 8 g/dL)

Q28. The chloride shift (Hamburger phenomenon) in red blood cells facilitates:

  • Movement of bicarbonate out of RBCs in exchange for chloride into RBCs
  • Movement of chloride out and bicarbonate into RBCs
  • Binding of O2 to hemoglobin
  • Formation of 2,3-BPG

Correct Answer: Movement of bicarbonate out of RBCs in exchange for chloride into RBCs

Q29. Which gas transport concept explains enhanced CO2 unloading in the lungs when blood becomes oxygenated?

  • Bohr effect
  • Haldane effect
  • Henry’s law
  • Fick’s law

Correct Answer: Haldane effect

Q30. In chronic obstructive pulmonary disease (COPD), which change is commonly seen regarding blood gases?

  • Chronic retention of CO2 with elevated PaCO2
  • Decreased PaCO2 compared to normal
  • Increased PaO2 due to hyperventilation
  • Absence of ventilation-perfusion mismatch

Correct Answer: Chronic retention of CO2 with elevated PaCO2

Q31. Oxygen-hemoglobin binding cooperativity is primarily due to:

  • Single independent binding sites on Hb
  • Conformational changes after O2 binding altering affinity of remaining sites
  • 2,3-BPG binding to heme iron
  • Irreversible binding of first O2 molecule

Correct Answer: Conformational changes after O2 binding altering affinity of remaining sites

Q32. Which laboratory finding suggests methemoglobinemia?

  • Chocolate-brown colored blood and low pulse oximeter saturation despite normal PaO2
  • Bright red blood and high PaO2
  • Elevated PaCO2 with low HCO3−
  • Low carboxyhemoglobin with normal SaO2

Correct Answer: Chocolate-brown colored blood and low pulse oximeter saturation despite normal PaO2

Q33. Which practice increases alveolar oxygen partial pressure (PAO2)?

  • Lowering FiO2
  • Increasing FiO2
  • Decreasing ventilation
  • Increasing physiologic shunt

Correct Answer: Increasing FiO2

Q34. Which statement about dissolved oxygen contribution to total O2 content is correct?

  • Dissolved O2 contributes the majority of O2 content
  • Dissolved O2 is negligible at normal PaO2 values compared to Hb-bound O2
  • Dissolved O2 increases dramatically with anemia
  • Dissolved O2 is independent of PaO2

Correct Answer: Dissolved O2 is negligible at normal PaO2 values compared to Hb-bound O2

Q35. Pulse oximetry estimates arterial oxygen saturation by measuring:

  • Partial pressure of O2 in plasma
  • Absorbance of light at two wavelengths to distinguish oxy- and deoxyhemoglobin
  • Total hemoglobin concentration directly
  • Bicarbonate levels

Correct Answer: Absorbance of light at two wavelengths to distinguish oxy- and deoxyhemoglobin

Q36. Which is true about oxygen delivery (DO2) to tissues?

  • DO2 = Cardiac output × arterial O2 content
  • DO2 is independent of hemoglobin concentration
  • DO2 decreases when cardiac output increases
  • DO2 equals venous O2 content only

Correct Answer: DO2 = Cardiac output × arterial O2 content

Q37. Which factor most increases the affinity of hemoglobin for O2?

  • Acidosis
  • Hypercapnia
  • Increased 2,3-BPG
  • Alkalosis

Correct Answer: Alkalosis

Q38. Which clinical scenario increases the proportion of CO2 carried as bicarbonate?

  • Low carbonic anhydrase activity
  • Rapid gas exchange in pulmonary capillaries
  • High CO2 production in tissues
  • Complete absence of chloride shift

Correct Answer: High CO2 production in tissues

Q39. Which gas has the greatest partial pressure in inspired air at sea level breathing room air?

  • Oxygen
  • Nitrogen
  • Carbon dioxide
  • Argon

Correct Answer: Nitrogen

Q40. In the context of gas transport, what is shunt?

  • Ventilated alveoli without perfusion
  • Perfused alveoli without ventilation leading to perfusion of non-oxygenated blood
  • Increased diffusion capacity
  • Enhanced oxygen solubility

Correct Answer: Perfused alveoli without ventilation leading to perfusion of non-oxygenated blood

Q41. Which inhaled anesthetic increases cerebral blood flow and may affect gas exchange clinically?

  • Propofol (IV)
  • Sevoflurane
  • Fentanyl (IV)
  • Succinylcholine (IV)

Correct Answer: Sevoflurane

Q42. What effect does anemia have on the oxygen-hemoglobin dissociation curve shape and oxygen content?

  • Curve shifts right and oxygen content increases
  • Curve unchanged but total oxygen content decreases
  • Curve shifts left and oxygen content increases
  • Curve becomes sigmoidal and oxygen content unaffected

Correct Answer: Curve unchanged but total oxygen content decreases

Q43. Which laboratory value best reflects ventilatory status rather than oxygenation?

  • PaO2
  • SaO2
  • PaCO2
  • Hemoglobin concentration

Correct Answer: PaCO2

Q44. Which of the following increases hemoglobin’s O2 unloading in exercising muscle?

  • Decreased temperature
  • Increased pH
  • Increased CO2, H+ and temperature
  • Decreased 2,3-BPG

Correct Answer: Increased CO2, H+ and temperature

Q45. Which parameter would be most helpful to detect cyanide poisoning effect on tissue oxygen utilization?

  • Elevated PaO2 with high mixed venous O2 content (reduced O2 extraction)
  • Low PaO2 with high oxygen extraction
  • Increased hemoglobin concentration
  • Decreased PaCO2 only

Correct Answer: Elevated PaO2 with high mixed venous O2 content (reduced O2 extraction)

Q46. In which condition is the oxygen-hemoglobin dissociation curve shifted RIGHT as a chronic adaptation?

  • Living at high altitude with increased 2,3-BPG
  • Newborn infant with predominant HbF
  • Chronic alkalosis
  • Acute hypothermia

Correct Answer: Living at high altitude with increased 2,3-BPG

Q47. Which statement about dissolved CO2 measurement is correct?

  • Dissolved CO2 is directly measured as PaCO2 on arterial blood gas
  • Dissolved CO2 is negligible compared to bicarbonate
  • Dissolved CO2 does not contribute to acid-base balance
  • PaCO2 does not reflect dissolved CO2

Correct Answer: Dissolved CO2 is directly measured as PaCO2 on arterial blood gas

Q48. Which effect does nitrites have that is dangerous for oxygen transport?

  • Reduce 2,3-BPG and improve O2 delivery
  • Convert hemoglobin to methemoglobin reducing O2 transport
  • Bind to heme increasing O2 affinity
  • Stimulate production of fetal hemoglobin

Correct Answer: Convert hemoglobin to methemoglobin reducing O2 transport

Q49. During exercise, what primarily increases oxygen delivery to skeletal muscle?

  • Decreased cardiac output
  • Increased capillary recruitment and blood flow to muscles
  • Decrease in muscle temperature
  • Increased hemoglobin oxidation to methemoglobin

Correct Answer: Increased capillary recruitment and blood flow to muscles

Q50. Which pharmacologic agent is used as an antidote for methemoglobinemia by reducing Fe3+ back to Fe2+?

  • Methylene blue
  • Nitroprusside
  • Sodium nitrite
  • Propranolol

Correct Answer: Methylene blue

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