Alveoli's adaptation for efficient gas exchange

Steps:

• Identify alveoli function: site of gas exchange in lungs via diffusion.
• Recall key adaptation: thin walls minimize diffusion distance for oxygen and CO2.
• Evaluate options: match to alveolar structure (squamous cells, no mucus/cilia/cartilage).
• Select best: A aligns with diffusion principle.

Why A is correct:

• Squamous epithelium is one cell thick, reducing diffusion distance per Fick's law (rate proportional to surface area and inversely to thickness).

Why the others are wrong:

• B: Goblet cells and mucus are in airways, not alveoli, to trap particles upstream.
• C: Ciliated epithelium is in bronchi, not alveoli, for mucus clearance.
• D: Cartilage supports larger airways, not flexible alveoli which rely on surfactant.

Final answer: A