Part 5: Transport of Oxygen in Blood (25 MCQs)

Q1. What percentage of oxygen is transported by hemoglobin in blood?

A. 3%
B. 23%
C. 70%
D. 97%

Answer: D

Explanation:

A. Incorrect: Dissolved O₂ is only ~3%.
B. Incorrect: 23% refers to CO₂ transport (carbaminoHb).
C. Incorrect: Not correct value.
D. Correct: ~97% O₂ carried by Hb as oxyhemoglobin.

Q2. One molecule of hemoglobin can carry how many oxygen molecules?

A. 1
B. 2
C. 3
D. 4

Answer: D

Explanation:

A. Incorrect: Too low.
B. Incorrect: Hb binds more.
C. Incorrect: Not correct.
D. Correct: Each Hb molecule (4 heme groups) binds 4 O₂.

Q3. The reversible binding of O₂ with hemoglobin depends mainly on:

A. pCO₂
B. pO₂
C. pH only
D. Temperature only

Answer: B

Explanation:

A. Incorrect: pCO₂ affects binding, but main factor is pO₂.
B. Correct: O₂ binding increases with higher pO₂.
C. Incorrect: pH is a modifying factor.
D. Incorrect: Temperature modifies affinity, not main driver.

Q4. The oxygen dissociation curve of hemoglobin is:

A. Linear
B. Sigmoid (S-shaped)
C. Hyperbolic
D. Straight line

Answer: B

Explanation:

A. Incorrect: Not linear.
B. Correct: Cooperative binding → sigmoid curve.
C. Incorrect: Hyperbolic for myoglobin, not Hb.
D. Incorrect: Not straight.

Q5. Which factor shifts the O₂ dissociation curve to the right?

A. Decrease in CO₂
B. Increase in pH
C. Increase in temperature
D. Decrease in 2,3-BPG

Answer: C

Explanation:

A. Incorrect: Less CO₂ shifts left.
B. Incorrect: High pH shifts left.
C. Correct: Higher temp decreases affinity, curve shifts right.
D. Incorrect: Decrease in 2,3-BPG shifts left.

Q6. The Bohr effect refers to:

A. Increase in O₂ affinity at low CO₂
B. Decrease in O₂ affinity at high CO₂ and low pH
C. Binding of CO to hemoglobin
D. Effect of surfactant on O₂ diffusion

Answer: B

Explanation:

A. Incorrect: That is opposite of Bohr effect.
B. Correct: Bohr effect → higher CO₂/lower pH reduces Hb-O₂ affinity.
C. Incorrect: CO poisoning is different.
D. Incorrect: Surfactant unrelated.

Q7. Myoglobin differs from hemoglobin in having:

A. Sigmoid curve
B. Hyperbolic O₂ dissociation curve
C. Less affinity for O₂
D. 4 heme groups

Answer: B

Explanation:

A. Incorrect: Hb shows sigmoid.
B. Correct: Myoglobin shows hyperbolic curve, high affinity.
C. Incorrect: Myoglobin has higher affinity, not less.
D. Incorrect: Myoglobin has 1 heme.

Q8. Which form of hemoglobin has highest affinity for oxygen?

A. Oxyhemoglobin
B. Carboxyhemoglobin
C. Methemoglobin
D. Fetal hemoglobin (HbF)

Answer: D

Explanation:

A. Incorrect: OxyHb binds O₂ but affinity lower than HbF.
B. Incorrect: CarboxyHb binds CO, not O₂.
C. Incorrect: Methemoglobin cannot carry O₂ efficiently.
D. Correct: HbF has greater O₂ affinity than adult HbA.

Q9. The percentage saturation of Hb with O₂ in venous blood is about:

A. 25%
B. 50%
C. 70–75%
D. 95%

Answer: C

Explanation:

A. Incorrect: Too low.
B. Incorrect: Not correct.
C. Correct: Venous Hb saturation ≈ 70–75%.
D. Incorrect: 95% = arterial blood.

Q10. The pO₂ in tissues at which Hb is 50% saturated is called:

A. Bohr point
B. P₅₀
C. Dead space
D. O₂ reserve

Answer: B

Explanation:

A. Incorrect: Not standard term.
B. Correct: P₅₀ = partial pressure at 50% saturation.
C. Incorrect: Dead space = non-exchanging air.
D. Incorrect: Not saturation point.

Q11. Increased levels of 2,3-bisphosphoglycerate (2,3-BPG) in RBCs:

A. Increase Hb affinity for O₂
B. Decrease Hb affinity for O₂
C. Have no effect on Hb-O₂ binding
D. Completely block O₂ transport

Answer: B

Explanation:

A. Incorrect: Affinity decreases, not increases.
B. Correct: More 2,3-BPG → Hb releases O₂ easily (right shift).
C. Incorrect: Has significant effect.
D. Incorrect: Does not block O₂.

Q12. What is the oxygen carrying capacity of 100 mL of blood?

A. 5 mL O₂
B. 10 mL O₂
C. 15 mL O₂
D. 20 mL O₂

Answer: D

Explanation:

A. Incorrect: Too low.
B. Incorrect: Below normal.
C. Incorrect: Underestimate.
D. Correct: Hb carries ~20 mL O₂/100 mL blood.

Q13. What happens to Hb affinity for O₂ at high altitude?

A. Increases due to low pCO₂
B. Decreases due to increased 2,3-BPG
C. Remains unchanged
D. Increases due to higher pO₂

Answer: B

Explanation:

A. Incorrect: Low pCO₂ effect is minor.
B. Correct: At altitude, 2,3-BPG rises → O₂ released easily.
C. Incorrect: Affinity does change.
D. Incorrect: pO₂ is lower at altitude.

Q14. Which condition shifts O₂ dissociation curve to the left?

A. Increased CO₂
B. Increased temperature
C. Increased pH
D. Increased 2,3-BPG

Answer: C

Explanation:

A. Incorrect: More CO₂ → right shift.
B. Incorrect: Higher temp → right shift.
C. Correct: High pH (alkalosis) increases O₂ affinity → left shift.
D. Incorrect: More 2,3-BPG → right shift.

Q15. Which type of hemoglobin is present in the fetus?

A. HbA
B. HbA₂
C. HbF
D. MetHb

Answer: C

Explanation:

A. Incorrect: HbA is adult form.
B. Incorrect: HbA₂ is minor adult type.
C. Correct: HbF (fetal hemoglobin) with higher O₂ affinity.
D. Incorrect: MetHb is abnormal.

Q16. Oxygen binding with Hb is favored by:

A. High pO₂, low pCO₂, high pH
B. Low pO₂, high pCO₂, low pH
C. High pO₂, high pCO₂, low pH
D. Low pO₂, low pCO₂, high pH

Answer: A

Explanation:

A. Correct: These conditions favor loading (lungs).
B. Incorrect: Opposite, favors unloading (tissues).
C. Incorrect: High CO₂ reduces binding.
D. Incorrect: Low pO₂ reduces binding.

Q17. At rest, tissues extract about what percentage of O₂ from Hb?

A. 10%
B. 25%
C. 50%
D. 75%

Answer: B

Explanation:

A. Incorrect: Too low.
B. Correct: At rest, tissues take ~25% O₂; venous Hb ~75% saturated.
C. Incorrect: 50% occurs during heavy exercise.
D. Incorrect: Not 75%.

Q18. Which protein helps store oxygen in muscle tissue?

A. Hemoglobin
B. Myoglobin
C. Globin
D. Cytochrome

Answer: B

Explanation:

A. Incorrect: Hb in blood, not storage.
B. Correct: Myoglobin stores O₂ in muscles.
C. Incorrect: Globin is Hb part, not storage.
D. Incorrect: Cytochromes transport electrons, not store O₂.

Q19. The plateau phase of O₂ dissociation curve ensures:

A. O₂ saturation remains high despite changes in alveolar pO₂
B. Rapid unloading of O₂ in tissues
C. CO₂ transport is unaffected
D. Hb has low affinity for O₂

Answer: A

Explanation:

A. Correct: Plateau maintains high Hb saturation even if alveolar pO₂ falls.
B. Incorrect: Rapid unloading occurs in steep part, not plateau.
C. Incorrect: Curve refers to O₂, not CO₂.
D. Incorrect: Affinity is high at plateau.

Q20. The steep portion of O₂ dissociation curve is physiologically important because:

A. It ensures O₂ loading in lungs
B. It facilitates O₂ unloading in tissues
C. It prevents Hb saturation
D. It increases blood pH

Answer: B

Explanation:

A. Incorrect: Loading occurs in plateau.
B. Correct: Steep slope helps tissues rapidly extract O₂.
C. Incorrect: Hb does saturate.
D. Incorrect: Curve doesn’t regulate pH.

Q21. Which abnormal form of Hb cannot bind O₂ efficiently?

A. OxyHb
B. CarboxyHb
C. CarbaminoHb
D. MetHb

Answer: D

Explanation:

A. Incorrect: OxyHb carries O₂ normally.
B. Incorrect: CarboxyHb binds CO, not O₂, but still abnormal binding.
C. Incorrect: CarbaminoHb carries CO₂.
D. Correct: Methemoglobin has oxidized Fe³⁺ → cannot carry O₂ effectively.

Q22. Which toxic gas competes with O₂ for binding to Hb with much higher affinity?

A. CO₂
B. CO
C. SO₂
D. NO₂

Answer: B

Explanation:

A. Incorrect: CO₂ binds but less strongly.
B. Correct: CO affinity ≈ 200–250× greater than O₂.
C. Incorrect: SO₂ irritates airways, doesn’t bind Hb.
D. Incorrect: NO₂ damages lungs but not bind Hb strongly.

Q23. Carbon monoxide poisoning causes:

A. Increased O₂ delivery to tissues
B. Decreased O₂ delivery due to stable carboxyHb
C. Increased O₂ affinity of Hb
D. No effect on O₂ transport

Answer: B

Explanation:

A. Incorrect: Opposite happens.
B. Correct: CO binds Hb strongly, prevents O₂ release.
C. Incorrect: Affinity for O₂ decreases in tissues.
D. Incorrect: Severe effect present.

Q24. The main advantage of cooperative binding of O₂ to Hb is:

A. Hb becomes saturated quickly in lungs
B. Hb never releases O₂
C. Hb binds O₂ linearly
D. Hb loses affinity completely in tissues

Answer: A

Explanation:

A. Correct: Cooperative binding → rapid O₂ loading in lungs.
B. Incorrect: O₂ is released in tissues.
C. Incorrect: Binding is sigmoid, not linear.
D. Incorrect: Affinity reduces but not completely lost.

Q25. In tissues with high metabolic activity, Hb releases more O₂ because:

A. Low CO₂ and low H⁺
B. High CO₂, low pH, high temperature
C. High pH and low temperature
D. Low CO₂ and high pH

Answer: B

Explanation:

A. Incorrect: Favors O₂ binding.
B. Correct: High CO₂, low pH (acidic), high temp → right shift (Bohr effect).
C. Incorrect: Alkaline and cold → left shift.
D. Incorrect: Favors binding, not release.

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Part 5: Transport of Oxygen in Blood (25 MCQs)