Phospholipids: lung surfactant: practice question

A Biochemistry 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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Biochemistry · Phospholipids: lung surfactant

Sample item

A neonate born at 30 weeks becomes tachypnoeic with grunting and chest retractions soon after birth. The chest radiograph shows a ground-glass appearance with air bronchograms. Which lipid is the principal component of the missing substance that lowers alveolar surface tension?

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

The answer and the reasoning

B. Dipalmitoylphosphatidylcholine

Type II pneumocytes synthesise surfactant, of which dipalmitoylphosphatidylcholine (dipalmitoyl lecithin) is the main surface-active lipid. It reduces surface tension and prevents alveolar collapse at end-expiration. Production matures late in gestation, and a lecithin to sphingomyelin ratio above 2 in amniotic fluid suggests lung maturity.

Option by option

  • A. Sphingomyelin

    Sphingomyelin is the denominator in the L/S ratio and stays constant, with no major role in surface tension.

  • B. Dipalmitoylphosphatidylcholine (correct)

    Dipalmitoyl lecithin is the main surface-active component of surfactant.

  • C. Cardiolipin

    Cardiolipin is found in the inner mitochondrial membrane.

  • D. Phosphatidylinositol bisphosphate

    Phosphatidylinositol bisphosphate is a membrane signalling lipid.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Dipalmitoylphosphatidylcholine. Type II pneumocytes synthesise surfactant, of which dipalmitoylphosphatidylcholine (dipalmitoyl lecithin) is the main surface-active lipid.

Why is "Sphingomyelin" not the answer?

Sphingomyelin is the denominator in the L/S ratio and stays constant, with no major role in surface tension.

Why is "Cardiolipin" not the answer?

Cardiolipin is found in the inner mitochondrial membrane.

Why is "Phosphatidylinositol bisphosphate" not the answer?

Phosphatidylinositol bisphosphate is a membrane signalling lipid.

What concept does this question test?

It tests Phospholipids: lung surfactant in Biochemistry. It reduces surface tension and prevents alveolar collapse at end-expiration. Production matures late in gestation, and a lecithin to sphingomyelin ratio above 2 in amniotic fluid suggests lung maturity.

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 Phospholipids: lung surfactant?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.