Final answer:
Water aspirated into the lungs causes a laryngeal spasm, preventing further water entry and reducing pneumonia risk; smokers are more susceptible due to impaired lung defenses.
Step-by-step explanation:
Water, if aspirated, is less likely to cause pneumonia because, during the early stages of drowning, a small amount of water entering the trachea triggers a laryngeal spasm that seals the airway and prevents water from reaching the lungs. The laryngeal spasm lasts until unconsciousness, reducing the risk of pneumonia, which is often caused by the presence of pathogens in water within the lungs.
Tobacco smoke, on the other hand, can impair lung immune defenses, making smokers more susceptible to pneumonia. Surfactant in the lungs reduces surface tension and is critical for lung function, highlighted by issues like hyaline membrane disease in newborns and emphysema. Additionally, the surface tension of water within the lungs is too great to allow for inhalation, further reducing the risk of pneumonia.