Question

If the inner surface of the ileum in the human small intestine was smooth, rather than being folded and subdivided into villi, which of the following statements would be true?

• A. The rate of absorption of digested food molecules would be higher, because the digested food would pass more easily through the digestive tract.
• B. Digestion would not be as effective, because there would be fewer cells secreting trypsin (a proteindigesting enzyme).
• C. Humans would have needed to evolve a much longer small intestine to absorb sufficient nutrients from their
  food.
• D. Humans would not be able to survive, because
  the digestive tract would be more susceptible to damage.

Answer 1

Answer: (C)

The wall of the alimentary canal has 4 layers. The innermost layer is called mucosa, whose function is to secrete mucus. The mucosa folds into finger-like foldings called as villi in the small intestine. The villi are connected with a network of capillaries and lymph. The largest of which is the lacteal. The cells that line the surface of villi produce numerous microscopic bristle-like projections called microvilli. The villi and microvilli increase the surface area of the small intestine to a great extent which helps in absorption of digested end products at a faster rate. If the inner surface of the ileum in the human small intestine was smooth, rather than being folded and subdivided into villi, then the extent of absorption will be decreased and the humans would have needed to evolve a much longer small intestine to absorb sufficient nutrients from their food.