Respiratory physiology: 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

Sample item

What happens to oxygen partial pressure as inspired air reaches humidified alveoli?

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

The answer and the reasoning

C. It falls because water vapour and carbon dioxide dilute inspired oxygen

Inspired oxygen pressure falls in humidified airways and further in alveoli because water vapour and carbon dioxide occupy part of the total gas pressure.

Option by option

  • A. It rises above atmospheric oxygen pressure

    Alveolar oxygen cannot exceed the dry inspired atmospheric value.

  • B. It becomes identical to venous oxygen pressure

    Venous oxygen is much lower than alveolar oxygen normally.

  • C. It falls because water vapour and carbon dioxide dilute inspired oxygen (correct)

    Correct: humidification and alveolar gas exchange reduce alveolar oxygen tension.

  • D. It is unaffected by ventilation

    Ventilation strongly influences alveolar gas composition.

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, It falls because water vapour and carbon dioxide dilute inspired oxygen. Inspired oxygen pressure falls in humidified airways and further in alveoli because water vapour and carbon dioxide occupy part of the total gas pressure.

Why is "It rises above atmospheric oxygen pressure" not the answer?

Alveolar oxygen cannot exceed the dry inspired atmospheric value.

Why is "It becomes identical to venous oxygen pressure" not the answer?

Venous oxygen is much lower than alveolar oxygen normally.

Why is "It is unaffected by ventilation" not the answer?

Ventilation strongly influences alveolar gas composition.

What concept does this question test?

It tests Respiratory physiology in Physiology. The correct option holds because: Correct: humidification and alveolar gas exchange reduce alveolar oxygen tension.

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?

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.