Respiratory physiology: oxygen content: 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 physiology: oxygen content

Sample item

A healthy adult has a haemoglobin of 15 g/dL and an arterial oxygen saturation of 100%. Ignoring dissolved oxygen, what is the approximate oxygen content of arterial blood? (Each gram of haemoglobin binds 1.34 mL of oxygen.)

A40 mL per dLB1.34 mL per dLC15 mL per dLD20 mL per dL

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

The answer and the reasoning

D. 20 mL per dL

Oxygen content is roughly 1.34 × haemoglobin × saturation = 1.34 × 15 × 1.0 ≈ 20 mL per dL. Dissolved oxygen adds only about 0.3 mL per dL at normal PaO2.

Option by option

A. 40 mL per dL
This is double the maximum content possible at this haemoglobin.
B. 1.34 mL per dL
This is the capacity of one gram of haemoglobin, not the content of a dL of blood.
C. 15 mL per dL
This equals the haemoglobin concentration in g/dL and ignores the binding factor of 1.34.
D. 20 mL per dL (correct)
Correct. 1.34 × 15 × 1.0 ≈ 20 mL per dL.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, 20 mL per dL. Oxygen content is roughly 1.

Why is "40 mL per dL" not the answer?

This is double the maximum content possible at this haemoglobin.

Why is "1.34 mL per dL" not the answer?

This is the capacity of one gram of haemoglobin, not the content of a dL of blood.

Why is "15 mL per dL" not the answer?

This equals the haemoglobin concentration in g/dL and ignores the binding factor of 1.34.

What concept does this question test?

It tests Respiratory physiology: oxygen content in Physiology. 34 × haemoglobin × saturation = 1.34 × 15 × 1.0 ≈ 20 mL per dL. Dissolved oxygen adds only about 0.3 mL per dL at normal PaO2.

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 physiology: oxygen content?

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.