Transport of respiratory gases MCQs With Answer

Transport of respiratory gases MCQs With Answer is an essential resource for B. Pharm students preparing for physiology, pharmacology, and clinical pharmacy exams. This concise guide focuses on oxygen and carbon dioxide transport mechanisms, hemoglobin function, oxygen dissociation curve, 2,3-BPG effects, Bohr and Haldane phenomena, forms of CO2 carriage, and clinical implications such as carboxyhemoglobinemia and methemoglobinemia. Clear explanations and targeted multiple-choice questions help reinforce core concepts, calculations of oxygen content, factors altering affinity, and gas exchange principles. Ideal for revision, test prep, and practical understanding, this set sharpens reasoning and application skills. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What percentage of oxygen in arterial blood is normally bound to hemoglobin?

• About 20%
• About 50%
• About 98%
• About 3%

Correct Answer: About 98%

Q2. Which form accounts for the largest fraction of carbon dioxide transport in blood?

• Dissolved CO2 in plasma
• Carbamino compounds bound to proteins
• As bicarbonate ions (HCO3-)
• Physically combined with oxygen

Correct Answer: As bicarbonate ions (HCO3-)

Q3. Which enzyme catalyzes the reversible hydration of CO2 to carbonic acid in red blood cells?

• Carbonic anhydrase
• Carboxylase
• Hemoglobinase
• Carbonyl reductase

Correct Answer: Carbonic anhydrase

Q4. The Bohr effect describes how which factors affect hemoglobin’s oxygen affinity?

• Decreased CO2 and increased pH increase affinity
• Increased CO2 and decreased pH decrease affinity
• Temperature and 2,3-BPG exclusively affect affinity
• Only partial pressure of nitrogen affects affinity

Correct Answer: Increased CO2 and decreased pH decrease affinity

Q5. What is the approximate P50 (partial pressure of O2 at 50% saturation) for adult hemoglobin under normal conditions?

• 5–8 mmHg
• 26–27 mmHg
• 60–70 mmHg
• 100 mmHg

Correct Answer: 26–27 mmHg

Q6. How does 2,3-bisphosphoglycerate (2,3-BPG) affect the oxygen-hemoglobin dissociation curve?

• Shifts curve to the left, increasing affinity
• Shifts curve to the right, decreasing affinity
• No effect on the curve
• Eliminates cooperative binding

Correct Answer: Shifts curve to the right, decreasing affinity

Q7. Which hemoglobin has higher oxygen affinity, fetal hemoglobin (HbF) or adult hemoglobin (HbA)?

• HbA has higher affinity
• HbF has higher affinity
• Both have identical affinities
• Affinity depends only on PaO2, not type

Correct Answer: HbF has higher affinity

Q8. Which phenomenon explains increased CO2 uptake by deoxygenated hemoglobin?

• Bohr effect
• Haldane effect
• Boiling effect
• Chaperone effect

Correct Answer: Haldane effect

Q9. Which of the following best describes the chloride shift?

• Exchange of Cl- for Na+ across RBC membrane
• Exchange of Cl- for HCO3- across RBC membrane
• Passive diffusion of chloride into alveoli
• Active transport of chloride into plasma via ATPase

Correct Answer: Exchange of Cl- for HCO3- across RBC membrane

Q10. What is the main effect of increased temperature on the oxyhemoglobin dissociation curve?

• Shift to the left (increased affinity)
• Shift to the right (decreased affinity)
• No change in curve position
• Increased cooperativity but unchanged position

Correct Answer: Shift to the right (decreased affinity)

Q11. Which value represents the normal oxygen content (CaO2) approximate formula component for hemoglobin-bound O2 (use Hb 15 g/dL and SaO2 100%)?

• 1.34 × Hb × SaO2 = 20.1 mL O2/dL
• 0.003 × PaO2 = 0.3 mL O2/dL
• 1.0 × Hb × SaO2 = 15 mL O2/dL
• 0.1 × PaO2 = 10 mL O2/dL

Correct Answer: 1.34 × Hb × SaO2 = 20.1 mL O2/dL

Q12. Which gas law explains the amount of gas dissolved in a liquid is proportional to its partial pressure?

• Boyle’s law
• Henry’s law
• Charles’s law
• Dalton’s law

Correct Answer: Henry’s law

Q13. Which condition causes a left shift of the oxygen-hemoglobin dissociation curve?

• Increased 2,3-BPG
• Decreased pH (acidosis)
• Decreased temperature
• Increased CO2

Correct Answer: Decreased temperature

Q14. Carboxyhemoglobin formation is caused by binding of CO to which site on hemoglobin?

• Iron in the heme group (Fe2+)
• Globin peptide backbone
• 2,3-BPG binding site
• Allosteric oxygen binding site only

Correct Answer: Iron in the heme group (Fe2+)

Q15. Which statement about methemoglobin is correct?

• Contains iron in the ferrous (Fe2+) state and binds oxygen normally
• Contains iron in the ferric (Fe3+) state and cannot bind oxygen effectively
• Is the same as carboxyhemoglobin
• Enhances oxygen delivery to tissues

Correct Answer: Contains iron in the ferric (Fe3+) state and cannot bind oxygen effectively

Q16. Which form of CO2 transport is responsible for the Bohr effect?

• Dissolved CO2 in plasma
• HCO3- generated by carbonic anhydrase
• Carbamino compounds bound to hemoglobin
• CO2 bound to myoglobin

Correct Answer: Carbamino compounds bound to hemoglobin

Q17. Which factor does NOT shift the oxygen dissociation curve to the right?

• Increased H+ concentration (lower pH)
• Increased 2,3-BPG
• Increased temperature
• Fetal hemoglobin predominance

Correct Answer: Fetal hemoglobin predominance

Q18. What is the primary reason fetal hemoglobin has higher O2 affinity than adult hemoglobin?

• Higher content of 2,3-BPG binding sites
• Different globin chains that reduce 2,3-BPG binding
• Higher body temperature in fetus
• Presence of myoglobin in fetal blood

Correct Answer: Different globin chains that reduce 2,3-BPG binding

Q19. Which statement about alveolar gas equation is correct?

• PAO2 = PaO2 + PaCO2/R
• PAO2 = PIO2 – (PaCO2/R)
• PAO2 = PaO2 × FiO2
• PAO2 = PaCO2 – (PIO2/R)

Correct Answer: PAO2 = PIO2 – (PaCO2/R)

Q20. Which measurement is commonly used clinically as an index of lung diffusing capacity for carbon monoxide?

• PaO2
• DLCO
• SpO2
• FEV1

Correct Answer: DLCO

Q21. What is the approximate solubility coefficient of oxygen in plasma (mL O2/dL blood/mmHg)?

• 0.003
• 0.03
• 0.3
• 1.34

Correct Answer: 0.003

Q22. Which clinical condition increases 2,3-BPG levels and shifts the curve right?

• Chronic hypoxia (e.g., high altitude)
• Acute hyperventilation
• Carbon monoxide poisoning
• Exposure to cold

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

Q23. Which statement best describes oxygen content (CaO2)?

• Depends only on PaO2 and not on hemoglobin
• Depends on hemoglobin concentration and SaO2 plus dissolved O2
• Is equal to oxygen saturation (SaO2) expressed as %
• Is determined solely by cardiac output

Correct Answer: Depends on hemoglobin concentration and SaO2 plus dissolved O2

Q24. During CO poisoning, pulse oximetry readings are often falsely normal because:

• CO2 displaces oxygen from hemoglobin
• Pulse oximeters cannot distinguish oxyhemoglobin from carboxyhemoglobin
• CO decreases PaO2 directly
• Carbaminohemoglobin affects the reading

Correct Answer: Pulse oximeters cannot distinguish oxyhemoglobin from carboxyhemoglobin

Q25. Which gas primarily determines oxygen diffusion driving force across the alveolar-capillary membrane?

• Alveolar nitrogen pressure
• Partial pressure difference of oxygen (PAO2 – PcO2)
• CO2 content in venous blood
• Hemoglobin concentration

Correct Answer: Partial pressure difference of oxygen (PAO2 – PcO2)

Q26. What percentage of CO2 is transported bound to hemoglobin as carbamino compounds approximately?

• Less than 1%
• ~20–23%
• ~70–75%
• ~100%

Correct Answer: ~20–23%

Q27. Which of the following increases oxygen unloading to tissues?

• Decreased CO2
• Alkalosis
• Increased 2,3-BPG
• Hypothermia

Correct Answer: Increased 2,3-BPG

Q28. Which clinical sign is more specific for impaired oxygen delivery due to hemoglobin abnormality?

• Tachycardia only
• Cyanosis despite normal PaO2
• Elevated PaCO2
• Hyperventilation with low PaO2

Correct Answer: Cyanosis despite normal PaO2

Q29. Which process in tissues converts CO2 to bicarbonate for transport?

• Spontaneous conversion without enzymes only
• Conversion by carbonic anhydrase in RBCs
• Conversion in plasma by hemoglobin
• Conversion in lungs only

Correct Answer: Conversion by carbonic anhydrase in RBCs

Q30. Which of the following best describes the Haldane effect?

• Oxygenation of hemoglobin increases its affinity for CO2
• Deoxygenated hemoglobin binds more CO2 and H+, facilitating CO2 transport
• CO2 decreases hemoglobin’s affinity for protons
• 2,3-BPG prevents CO2 binding to hemoglobin

Correct Answer: Deoxygenated hemoglobin binds more CO2 and H+, facilitating CO2 transport

Q31. Which of the following is TRUE about myoglobin compared to hemoglobin?

• Myoglobin has lower O2 affinity than hemoglobin
• Myoglobin facilitates O2 storage in muscle with higher affinity
• Myoglobin is tetrameric like hemoglobin
• Myoglobin exhibits cooperative binding

Correct Answer: Myoglobin facilitates O2 storage in muscle with higher affinity

Q32. Which factor most increases oxygen delivery (DO2) to tissues?

• Decreased cardiac output
• Increased hemoglobin concentration
• Lower arterial oxygen content
• Decreased arterial saturation

Correct Answer: Increased hemoglobin concentration

Q33. What effect does respiratory alkalosis have on oxygen-hemoglobin affinity?

• Shifts curve to the right (decreases affinity)
• Shifts curve to the left (increases affinity)
• No effect on affinity
• Causes hemoglobin to release CO2 instead

Correct Answer: Shifts curve to the left (increases affinity)

Q34. Which clinical test directly measures carboxyhemoglobin and methemoglobin levels?

• Standard pulse oximetry
• Co-oximetry (multi-wavelength oximeter)
• Capnography
• Arterial blood gas without co-oximetry

Correct Answer: Co-oximetry (multi-wavelength oximeter)

Q35. Which of the following shifts the oxyhemoglobin curve to the right enhancing tissue O2 release during exercise?

• Decreased muscle temperature
• Decreased CO2 production
• Increased lactic acid and increased temperature
• Decreased 2,3-BPG in erythrocytes

Correct Answer: Increased lactic acid and increased temperature

Q36. Which statement about dissolved oxygen in blood is correct?

• Dissolved O2 contributes the majority of oxygen content
• Dissolved O2 is directly proportional to PaO2 via solubility coefficient
• Dissolved O2 binds to hemoglobin
• Dissolved O2 is unaffected by PaO2

Correct Answer: Dissolved O2 is directly proportional to PaO2 via solubility coefficient

Q37. Which condition produces a left shift and makes oxygen unloading to tissues more difficult?

• Acidosis
• Fever
• Carbon monoxide poisoning
• High 2,3-BPG

Correct Answer: Carbon monoxide poisoning

Q38. Which ion transport is essential to maintain electroneutrality during the chloride shift?

• Sodium influx paired with potassium efflux
• Chloride influx paired with bicarbonate efflux
• Chloride influx paired with bicarbonate efflux
• Chloride influx paired with bicarbonate efflux

Correct Answer: Chloride influx paired with bicarbonate efflux

Q39. Which of the following best describes oxygen delivery to tissues (DO2)?

• DO2 = Cardiac output × Arterial oxygen content
• DO2 = Venous oxygen content × Respiratory rate
• DO2 = PaO2 × Hemoglobin
• DO2 = FIO2 × Tidal volume

Correct Answer: DO2 = Cardiac output × Arterial oxygen content

Q40. Which measurement indicates how well oxygen diffuses from alveoli into blood?

• DLCO (diffusing capacity for CO)
• FEV1/FVC ratio
• PaCO2 only
• SpO2 only

Correct Answer: DLCO (diffusing capacity for CO)

Q41. Which process predominates in CO2 conversion back to CO2 in pulmonary capillaries?

• HCO3- converted to CO2 by carbonic anhydrase within RBCs
• Direct passive diffusion of bicarbonate
• Conversion of CO2 to carbonic acid in plasma
• Binding of CO2 to 2,3-BPG

Correct Answer: HCO3- converted to CO2 by carbonic anhydrase within RBCs

Q42. Which statement about oxygen-hemoglobin cooperativity is correct?

• Binding of one O2 decreases affinity for subsequent O2 molecules
• Hemoglobin displays non-cooperative, independent binding sites
• Binding of one O2 increases affinity for additional O2 molecules
• Cooperativity only occurs in fetal hemoglobin

Correct Answer: Binding of one O2 increases affinity for additional O2 molecules

Q43. What happens to arterial oxygen content when hemoglobin level falls but PaO2 remains normal?

• Arterial oxygen content decreases
• Arterial oxygen content increases
• No change in arterial oxygen content
• PaO2 will fall immediately

Correct Answer: Arterial oxygen content decreases

Q44. Which therapy is most appropriate for acute carbon monoxide poisoning?

• Nitric oxide inhalation
• 100% oxygen therapy or hyperbaric oxygen
• High-flow nitrogen
• Low-flow room air only

Correct Answer: 100% oxygen therapy or hyperbaric oxygen

Q45. Which clinical scenario increases the dissolved fraction of O2 significantly?

• Administration of 100% oxygen increases PaO2 greatly, raising dissolved O2
• Decrease in PaO2 increases dissolved O2
• Decrease in atmospheric pressure increases dissolved O2
• Increasing hemoglobin concentration raises dissolved O2

Correct Answer: Administration of 100% oxygen increases PaO2 greatly, raising dissolved O2

Q46. Which compound stabilizes the deoxy form of hemoglobin and promotes oxygen release?

• Oxygen
• 2,3-BPG
• Carbon monoxide
• Glucose

Correct Answer: 2,3-BPG

Q47. Which of the following is true about arterial-venous oxygen difference (A–V O2 diff)?

• It narrows during exercise
• It widens during increased tissue extraction of O2
• It is independent of cardiac output
• It is higher when hemoglobin concentration increases

Correct Answer: It widens during increased tissue extraction of O2

Q48. Which of the following reduces hemoglobin’s ability to carry oxygen by oxidizing iron?

• Formation of carbaminohemoglobin
• Formation of methemoglobin
• Binding of oxygen to ferrous iron
• Increased 2,3-BPG

Correct Answer: Formation of methemoglobin

Q49. How does anemia affect oxygen delivery if cardiac output does not change?

• Oxygen delivery increases due to compensation
• Oxygen delivery decreases because arterial content falls
• No change in oxygen delivery because PaO2 is preserved
• Only PaCO2 changes, not oxygen delivery

Correct Answer: Oxygen delivery decreases because arterial content falls

Q50. Which factor most directly increases unloading of O2 from hemoglobin in actively metabolizing tissues?

• Decreased temperature and decreased CO2
• Increased pH and decreased 2,3-BPG
• Increased CO2, increased H+, and increased temperature
• Decreased metabolic activity

Correct Answer: Increased CO2, increased H+, and increased temperature

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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