Which statement regarding the normal microbiota of the human respiratory system is false?

• A. Normal microbiota in the upper respiratory tract can help prevent colonization by pathogens.
• B. The lower respiratory tract is generally free of permanent microbiota in healthy individuals.
• C. Disruption of normal microbiota in the respiratory tract can increase susceptibility to infections.
• D. All regions of the respiratory system, including the alveoli, are densely populated with microbiota.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the concept of normal microbiota in the respiratory system. Normal microbiota are microorganisms that reside in specific areas of the body without causing disease and often provide protective benefits against pathogens.
2. Step 2: Review the distribution of microbiota in the respiratory tract. The upper respiratory tract (nose, pharynx) typically harbors a diverse community of microorganisms, while the lower respiratory tract (trachea, bronchi, alveoli) is usually sterile or has very few microbes in healthy individuals.
3. Step 3: Analyze each statement in the problem: - The first statement says normal microbiota in the upper respiratory tract help prevent pathogen colonization, which is true because they compete with harmful microbes. - The second statement claims the lower respiratory tract is generally free of permanent microbiota in healthy people, which aligns with current scientific understanding. - The third statement notes that disruption of normal microbiota can increase infection risk, which is also true as it reduces microbial competition and immune stimulation. - The fourth statement claims all regions, including alveoli, are densely populated with microbiota, which contradicts the known fact that alveoli are normally sterile or nearly sterile.
4. Step 4: Identify the false statement by comparing it to established microbiological knowledge. Since the alveoli and lower respiratory tract are not densely populated with microbiota, the fourth statement is false.
5. Step 5: Summarize the reasoning: The false statement is the one that incorrectly claims dense microbiota presence in all respiratory regions, including alveoli, because healthy lower respiratory tract areas are typically free of permanent microbiota.