The villus in the small intestine is significant because

Step 1: Analyze the question The question asks about the significance (function) of the villi in the small intestine.

Step 2: The concept The inner wall of the small intestine, especially the ileum, is folded and lined with tiny finger-like projections called villi (singular: villus). Each villus has:

• A thin wall, one cell thick (epithelium), for short diffusion distance
• A rich network of blood capillaries to carry away absorbed glucose and amino acids
• A lacteal (lymph vessel) to carry away fatty acids and glycerol
• Microvilli on the surface cells, which increase the area even further

Digestion is done by enzymes in the lumen of the gut, not by the villi. The villi are built for absorption.

Step 3: Evaluate the options

• A. Increases the surface area for absorption. Correct. More surface area means more digested food can be absorbed into the blood and lymph faster.
• B. Increases the surface area for digestion. Wrong. Digestion is carried out by enzymes, and the villi's job is absorption.
• C. Assists in mixing digested food. Wrong. Mixing is done by peristalsis and segmentation, which are muscular movements.
• D. Assists in filtering undigested food. Wrong. The villi do not filter anything. Undigested material moves on to the large intestine.

Step 4: Answer The villi increase the surface area for absorption of digested food, so the answer is A.

Exam tip: Remember "Villi = Very large area for absorption." Whenever you see structures that increase surface area (villi in the ileum, alveoli in the lungs, root hairs in plants), think of absorption or exchange, not digestion.