A Level Biology Practice Exam 2026 - Free A Level Biology Practice Questions and Study Guide

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What components are primarily found in lung surfactant?

Carbohydrates and proteins

Water and salts

Phospholipids and proteins

Lung surfactant is primarily composed of phospholipids and proteins, with the most abundant phospholipid being dipalmitoylphosphatidylcholine (DPPC). This composition is crucial because surfactant plays an essential role in reducing surface tension in the alveoli, the tiny air sacs in the lungs where gas exchange occurs. By lowering surface tension, surfactant helps prevent the alveoli from collapsing during exhalation and ensures that they expand efficiently during inhalation.

The proteins found in lung surfactant, known as surfactant proteins (SPs), facilitate the spreading and stability of the phospholipids and also play a role in immune defense within the lungs. Overall, the combination of phospholipids and proteins allows lung surfactant to fulfill its critical functions in respiratory physiology effectively.

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Nucleic acids and lipids

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