Respiratory system: Haldane effect: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Respiratory system: Haldane effect

Sample item

In the pulmonary capillaries, oxygenation of haemoglobin promotes the release of CO2 from blood. Which explanation is correct?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Oxyhaemoglobin is a stronger acid, so it releases H+ and carbamino CO2, driving bicarbonate to CO2

The Haldane effect states that oxygenated blood carries less CO2 than deoxygenated blood at the same PCO2. Oxyhaemoglobin has a lower affinity for H+ and for CO2 than deoxyhaemoglobin, so H+ is released, combines with bicarbonate and yields CO2 that is exhaled.

Option by option

  • A. Oxyhaemoglobin binds H+ more avidly than deoxyhaemoglobin, favouring bicarbonate formation

    Deoxyhaemoglobin, not oxyhaemoglobin, binds H+ more avidly, which is why venous blood carries more CO2.

  • B. Oxygenation shifts the oxygen dissociation curve rightward, which expels CO2

    A rightward shift of the curve is the Bohr effect, a separate phenomenon concerning oxygen unloading.

  • C. Oxyhaemoglobin is a stronger acid, so it releases H+ and carbamino CO2, driving bicarbonate to CO2 (correct)

    The stronger acidity of oxyhaemoglobin pushes the reaction toward CO2 formation.

  • D. Oxygen directly displaces CO2 dissolved in plasma by competing for physical solution

    Gases do not displace one another from physical solution; each follows its own partial pressure.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Oxyhaemoglobin is a stronger acid, so it releases H+ and carbamino CO2, driving bicarbonate to CO2. The Haldane effect states that oxygenated blood carries less CO2 than deoxygenated blood at the same PCO2.

Why is "Oxyhaemoglobin binds H+ more avidly than deoxyhaemoglobin, favouring…" not the answer?

Deoxyhaemoglobin, not oxyhaemoglobin, binds H+ more avidly, which is why venous blood carries more CO2.

Why is "Oxygenation shifts the oxygen dissociation curve rightward, which exp…" not the answer?

A rightward shift of the curve is the Bohr effect, a separate phenomenon concerning oxygen unloading.

Why is "Oxygen directly displaces CO2 dissolved in plasma by competing for ph…" not the answer?

Gases do not displace one another from physical solution; each follows its own partial pressure.

What concept does this question test?

It tests Respiratory system: Haldane effect in Physiology. Oxyhaemoglobin has a lower affinity for H+ and for CO2 than deoxyhaemoglobin, so H+ is released, combines with bicarbonate and yields CO2 that is exhaled.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Respiratory system: Haldane effect?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.