Villi Boost Nutrient Absorption via Diffusion

Steps:

• Identify the role of villi: they fold the intestinal lining to increase surface area.
• Recall absorption process: digested nutrients diffuse across the epithelium into blood vessels.
• Link surface area to diffusion: larger area allows more molecules to contact and cross the membrane.
• Evaluate choices: select the one directly tying increased area to diffusion efficiency.

Why D is correct:

• Diffusion follows Fick's law, where rate is proportional to surface area; larger area from villi increases nutrient molecule diffusion into blood capillaries.

Why the others are wrong:

• A: Peristalsis moves food via muscle contractions, unrelated to surface area.
• B: Absorption isn't limited by nutrient type but by contact area for diffusion.
• C: Mucus aids lubrication, produced by goblet cells, not affected by villi surface.

Final answer: D