Exchange of gases MCQs With Answer

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Exchange of gases MCQs With Answer – This compact, SEO-friendly introduction helps B. Pharm students master respiratory physiology and clinical implications of gas exchange. Covering key topics such as alveolar ventilation, partial pressures, Fick’s law, oxygen and carbon dioxide transport, hemoglobin affinity, the oxygen dissociation curve, Bohr effect, 2,3-BPG, diffusion limitations, ventilation-perfusion mismatch, and pathological states (COPD, shunt, high altitude, CO poisoning), these MCQs reinforce pharmacology-relevant concepts and drug effects on gas transport. Clear explanations build understanding for exams and clinical practice. Focused keywords include gas exchange, respiratory physiology, oxygen transport, CO2 transport, hemoglobin, and Exchange of gases MCQs With Answer. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which law explains the amount of a gas that dissolves in a liquid at a given temperature is proportional to its partial pressure?

  • Fick’s law
  • Henry’s law
  • Boyle’s law
  • Dalton’s law

Correct Answer: Henry’s law

Q2. According to Fick’s law of diffusion, which factor does NOT directly affect the rate of gas diffusion across the alveolar membrane?

  • Surface area of the membrane
  • Thickness of the membrane
  • Partial pressure difference of the gas
  • Hemoglobin concentration in blood

Correct Answer: Hemoglobin concentration in blood

Q3. Which form carries the greatest proportion of carbon dioxide from tissues to lungs?

  • Dissolved CO2 in plasma
  • Carbaminohemoglobin
  • Bicarbonate ion (HCO3−)
  • Carbonic acid (H2CO3)

Correct Answer: Bicarbonate ion (HCO3−)

Q4. The primary site of gas exchange in the lung is:

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli

Correct Answer: Alveoli

Q5. Which factor shifts the oxygen-hemoglobin dissociation curve to the right, facilitating oxygen unloading?

  • Decreased temperature
  • Decreased 2,3-BPG
  • Increased hydrogen ion concentration (lower pH)
  • Fetal hemoglobin predominance

Correct Answer: Increased hydrogen ion concentration (lower pH)

Q6. The Bohr effect primarily describes how which variable influences hemoglobin’s oxygen affinity?

  • CO2 concentration and pH
  • Body temperature
  • Glucose level
  • Plasma osmolarity

Correct Answer: CO2 concentration and pH

Q7. Which statement about alveolar gas equation is correct?

  • It calculates arterial CO2 from alveolar O2
  • It estimates alveolar O2 tension based on FiO2, PaCO2, and R
  • It directly measures oxygen content in blood
  • It is independent of respiratory quotient

Correct Answer: It estimates alveolar O2 tension based on FiO2, PaCO2, and R

Q8. Which condition results in reduced diffusion capacity for carbon monoxide (DLCO) due to decreased surface area?

  • Pulmonary fibrosis
  • Emphysema
  • Pulmonary edema
  • Asthma

Correct Answer: Emphysema

Q9. Which transport form of oxygen is quantitatively most important in blood?

  • Dissolved oxygen in plasma
  • Oxygen chemically bound to bicarbonate
  • Oxygen bound to hemoglobin
  • Oxygen stored in leukocytes

Correct Answer: Oxygen bound to hemoglobin

Q10. Carbon monoxide (CO) poisoning impairs oxygen transport primarily by:

  • Blocking alveolar ventilation
  • Oxidizing hemoglobin to methemoglobin
  • Competing with oxygen for hemoglobin binding sites
  • Increasing dissolved oxygen solubility

Correct Answer: Competing with oxygen for hemoglobin binding sites

Q11. Which describes the chloride shift (Hamburger phenomenon)?

  • Chloride moves into RBCs as HCO3− moves out
  • Chloride moves out of RBCs as HCO3− moves in
  • Chloride influx causes hemoglobin to release CO2
  • Chloride binds CO2 directly in plasma

Correct Answer: Chloride moves into RBCs as HCO3− moves out

Q12. The oxygen content of arterial blood (CaO2) depends on which two main components?

  • PaO2 and PCO2
  • Hemoglobin concentration and SaO2
  • Alveolar ventilation and dead space
  • FRC and TLC

Correct Answer: Hemoglobin concentration and SaO2

Q13. 2,3-Bisphosphoglycerate (2,3-BPG) in red cells affects oxygen binding by:

  • Increasing hemoglobin’s affinity for oxygen
  • Decreasing hemoglobin’s affinity for oxygen
  • Converting hemoglobin to methemoglobin
  • Binding oxygen directly in plasma

Correct Answer: Decreasing hemoglobin’s affinity for oxygen

Q14. Which change occurs at high altitude to improve oxygen delivery?

  • Decreased ventilation
  • Increased 2,3-BPG production
  • Decreased hemoglobin concentration
  • Left shift of oxyhemoglobin curve

Correct Answer: Increased 2,3-BPG production

Q15. Which of the following best characterizes a right-to-left intrapulmonary shunt?

  • Well ventilated alveoli with no perfusion
  • Perfused alveoli with little or no ventilation
  • Increased alveolar dead space
  • Low perfusion pressure causing hypoventilation

Correct Answer: Perfused alveoli with little or no ventilation

Q16. Pulse oximetry may give falsely normal oxygen saturation in which condition?

  • Methemoglobinemia
  • Anemia with low SaO2
  • Hypoventilation with low PaCO2
  • Hyperoxia from supplemental O2

Correct Answer: Methemoglobinemia

Q17. Which gas law explains that total pressure of a gas mixture equals the sum of partial pressures?

  • Henry’s law
  • Dalton’s law
  • Charles’s law
  • Avogadro’s law

Correct Answer: Dalton’s law

Q18. In hypoventilation, the primary change leading to hypoxemia is:

  • Increase in alveolar O2 due to trapping
  • Decrease in alveolar and arterial O2 due to raised PaCO2
  • Improved V/Q matching
  • Increased diffusion capacity

Correct Answer: Decrease in alveolar and arterial O2 due to raised PaCO2

Q19. Which condition primarily decreases DLCO because of increased membrane thickness?

  • Emphysema
  • Pulmonary fibrosis
  • Pulmonary embolism
  • Asthma exacerbation

Correct Answer: Pulmonary fibrosis

Q20. Carbaminohemoglobin forms when CO2 binds to which part of hemoglobin?

  • Heme iron
  • Globin amino groups
  • 2,3-BPG binding site
  • Oxygen-binding pocket

Correct Answer: Globin amino groups

Q21. Which factor increases oxygen delivery to tissues despite low arterial oxygen partial pressure?

  • Low cardiac output
  • Increased hemoglobin concentration
  • Decreased perfusion pressure
  • Left shift of oxyhemoglobin curve

Correct Answer: Increased hemoglobin concentration

Q22. The A-a gradient is useful for distinguishing which two causes of hypoxemia?

  • Anemia and polycythemia
  • Hypoventilation and V/Q mismatch/shunt
  • Hypercapnia and hypocapnia
  • Metabolic acidosis and alkalosis

Correct Answer: Hypoventilation and V/Q mismatch/shunt

Q23. Which drug or agent is most associated with inducing methemoglobinemia, affecting oxygen delivery?

  • Nitrites and local anesthetics like benzocaine
  • Beta blockers
  • ACE inhibitors
  • Statins

Correct Answer: Nitrites and local anesthetics like benzocaine

Q24. Which describes “physiologic dead space”?

  • Volume of gas in alveoli not participating in gas exchange (ventilated but not perfused)
  • Volume of gas trapped in pleural space
  • Space occupied by conducting airways that are perfused
  • Volume of blood not participating in gas exchange

Correct Answer: Volume of gas in alveoli not participating in gas exchange (ventilated but not perfused)

Q25. Which is true about fetal hemoglobin (HbF) compared to adult hemoglobin (HbA)?

  • HbF has lower affinity for oxygen than HbA
  • HbF binds 2,3-BPG more strongly
  • HbF has higher oxygen affinity to facilitate maternal-fetal transfer
  • HbF forms carbamino compounds preferentially

Correct Answer: HbF has higher oxygen affinity to facilitate maternal-fetal transfer

Q26. Which is the primary compensatory respiratory response to metabolic acidosis?

  • Hypoventilation to retain CO2
  • Hyperventilation to blow off CO2
  • Increase in bicarbonate secretion
  • Decrease in respiratory rate variability only

Correct Answer: Hyperventilation to blow off CO2

Q27. In COPD patients with chronic CO2 retention, a sudden increase in inspired oxygen can cause:

  • Decreased PaCO2 and improved ventilation
  • No change in ventilation or gas exchange
  • Worsening hypercapnia due to loss of hypoxic drive and V/Q effects
  • Immediate elimination of V/Q mismatch

Correct Answer: Worsening hypercapnia due to loss of hypoxic drive and V/Q effects

Q28. Which index quantifies the efficiency of ventilation for CO2 elimination?

  • Alveolar-arterial gradient
  • Minute ventilation (VE)
  • Dead space fraction (VD/VT)
  • Oxygen extraction ratio

Correct Answer: Dead space fraction (VD/VT)

Q29. Anemia causes hypoxia primarily by:

  • Decreasing PaO2
  • Lowering hemoglobin concentration and thus oxygen content
  • Impairing alveolar ventilation directly
  • Increasing hemoglobin’s oxygen affinity

Correct Answer: Lowering hemoglobin concentration and thus oxygen content

Q30. Which measurement directly assesses oxygen dissolved in plasma?

  • SaO2 by pulse oximetry
  • PaO2 from arterial blood gas
  • Hemoglobin concentration
  • Oxygen content (CaO2)

Correct Answer: PaO2 from arterial blood gas

Q31. Which process accelerates CO2 conversion to bicarbonate within red blood cells?

  • Hemoglobin binding
  • Carbonic anhydrase enzyme
  • 2,3-BPG presence
  • Plasma cholinesterase

Correct Answer: Carbonic anhydrase enzyme

Q32. Right shift of oxyhemoglobin curve can be produced by all EXCEPT:

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

Correct Answer: Fetal hemoglobin predominance

Q33. Which best describes ventilation-perfusion (V/Q) ratio in a normal healthy lung on average?

  • Approximately 0.5
  • Approximately 1.0
  • Approximately 5.0
  • Zero

Correct Answer: Approximately 1.0

Q34. Which condition increases diffusion limitation for oxygen, especially during exercise?

  • Pulmonary embolism
  • Anemia
  • Pulmonary fibrosis
  • Bronchitis

Correct Answer: Pulmonary fibrosis

Q35. How does methemoglobin affect oxygen delivery?

  • Enhances O2 release to tissues
  • Decreases oxygen-carrying capacity and shifts curve left, impairing delivery
  • Has no effect on oxygen transport
  • Increases PaO2 readings on ABG

Correct Answer: Decreases oxygen-carrying capacity and shifts curve left, impairing delivery

Q36. In carbonic anhydrase deficiency, which gas transport step is impaired?

  • Dissolution of O2 in plasma
  • Conversion of CO2 to bicarbonate inside RBCs
  • Hemoglobin synthesis
  • Alveolar ventilation

Correct Answer: Conversion of CO2 to bicarbonate inside RBCs

Q37. Which statement about CO2 solubility compared to O2 is correct?

  • CO2 is less soluble than O2 in plasma
  • CO2 is about 20 times more soluble than O2 in plasma
  • CO2 and O2 have identical solubility
  • O2 is more soluble than CO2

Correct Answer: CO2 is about 20 times more soluble than O2 in plasma

Q38. Which pharmacologic agent can reduce pulmonary vascular resistance and improve V/Q matching in certain disorders?

  • Inhaled nitric oxide
  • Systemic beta blockers
  • IV epinephrine at low dose
  • Oral diuretics

Correct Answer: Inhaled nitric oxide

Q39. Which best explains “acute right-to-left shunt” effect on oxygenation?

  • Hyperventilation corrects hypoxemia fully
  • Supplemental oxygen has limited effect because blood bypasses ventilated alveoli
  • Dead space ventilation increases oxygenation
  • CO2 elimination is enhanced

Correct Answer: Supplemental oxygen has limited effect because blood bypasses ventilated alveoli

Q40. Which gas transport abnormality is characteristic of chronic bronchitis?

  • Markedly reduced DLCO
  • Hypoxemia with hypercapnia from V/Q mismatch
  • Polycythemia due to decreased CO2
  • Excessive O2 saturation despite hypoventilation

Correct Answer: Hypoxemia with hypercapnia from V/Q mismatch

Q41. Which factor most directly determines oxygen saturation at a given PaO2?

  • Hemoglobin concentration
  • Shape and position of the oxyhemoglobin dissociation curve
  • Cardiac output
  • Blood viscosity

Correct Answer: Shape and position of the oxyhemoglobin dissociation curve

Q42. Which clinical measure estimates alveolar ventilation?

  • Tidal volume alone
  • Minute ventilation times respiratory quotient
  • Alveolar ventilation = (VT − VD) × respiratory rate
  • Dead space volume only

Correct Answer: Alveolar ventilation = (VT − VD) × respiratory rate

Q43. Which describes the effect of sepsis on pulmonary gas exchange?

  • Improved V/Q matching and increased PaO2
  • Increased pulmonary capillary permeability causing edema and diffusion impairment
  • Reduced cardiac output only with no lung effect
  • Permanent increase in DLCO

Correct Answer: Increased pulmonary capillary permeability causing edema and diffusion impairment

Q44. Which laboratory finding is consistent with hypoventilation?

  • Low PaCO2 and alkalemia
  • High PaCO2 and respiratory acidosis
  • High PaO2 and low PaCO2
  • Normal PaCO2 with metabolic alkalosis

Correct Answer: High PaCO2 and respiratory acidosis

Q45. Which mechanism increases oxygen unloading during exercise?

  • Decrease in temperature and increase in pH
  • Increase in temperature, CO2, and H+ (right shift)
  • Decrease in 2,3-BPG levels
  • Fetal hemoglobin production

Correct Answer: Increase in temperature, CO2, and H+ (right shift)

Q46. Which is the most appropriate immediate treatment for severe carbon monoxide poisoning?

  • Pulse oximetry monitoring only
  • High-flow 100% oxygen or hyperbaric oxygen therapy
  • Administration of methylene blue
  • Ventilation with low FiO2

Correct Answer: High-flow 100% oxygen or hyperbaric oxygen therapy

Q47. Which of the following increases the A–a gradient?

  • Pure hypoventilation without lung disease
  • Right-to-left shunt and V/Q mismatch
  • Decreased inspired oxygen with intact lungs
  • High altitude causing low atmospheric oxygen

Correct Answer: Right-to-left shunt and V/Q mismatch

Q48. Which parameter remains relatively normal in early interstitial lung disease despite impaired gas exchange?

  • DLCO
  • TLC
  • PaO2 during exercise
  • Resting PaO2 may be near normal but DLCO is reduced

Correct Answer: Resting PaO2 may be near normal but DLCO is reduced

Q49. Cyanide poisoning impairs cellular oxygen utilization primarily by inhibiting:

  • Hemoglobin synthesis
  • Cytochrome c oxidase in the electron transport chain
  • Pulmonary surfactant production
  • Carbonic anhydrase activity

Correct Answer: Cytochrome c oxidase in the electron transport chain

Q50. Which intervention increases arterial oxygen content (CaO2) most effectively in a patient with severe anemia?

  • Supplemental oxygen alone
  • Transfusion of packed red blood cells
  • Administration of bronchodilators
  • Inhaled nitric oxide

Correct Answer: Transfusion of packed red blood cells

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