Concept:The villus is a tiny finger-like structure lining the small intestine that improves nutrient uptake.
Explanation:The inner wall of the small intestine contains millions of villi.
Each villus projects into the intestinal lumen and greatly increases the internal surface area of the intestine.
A larger surface area allows more digested food molecules, such as amino acids and glucose, to come into contact with the absorbing walls.
This contact speeds up the movement of nutrients into the bloodstream and lymphatic system.
Villi do not directly increase the surface for digestion, mix food, or filter undigested material.
Therefore, the key significance of the villus is to maximise absorption of digested food.
Answer:A. increases the surface area for absorption.