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?

Options

A. a) The rate of absorption of digested food molecules would be higher, because the digested food would pass more easily thorugh the digestive tract.
B. b) Digestion would not be as effective, because there would be fewer cells scretting trypsin (a protein-digesting enzyme).
C. c) Humans would have needed to evolve a much longer small intesntine to absorb sufficient nutrients from their food.
D. d) Humans would not be able to survive, because the digestive tract would be more susceptible to damage.

Explanation

To solve the question regarding the implications of a smooth inner surface of the ileum in the human small intestine, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of the Ileum**: The ileum is the final part of the small intestine and is characterized by its highly folded inner surface, which includes structures called villi. These structures significantly increase the surface area available for absorption.

2. **Function of Villi and Folds**: The folds and villi in the ileum serve to maximize the surface area, allowing for more efficient absorption of nutrients from digested food. The presence of these structures is crucial for effective nutrient absorption.

3. **Consequences of a Smooth Surface**: If the inner surface of the ileum were smooth, it would mean the absence of folds and villi. This would drastically reduce the surface area available for absorption.

4. **Impact on Nutrient Absorption**: With a reduced surface area, the efficiency of nutrient absorption would be compromised. The small intestine would not be able to absorb sufficient nutrients from the food consumed.

5. **Evaluating the Statements**:
- **Statement A**: "The rate of absorption of digested food molecules would be higher." This is incorrect because a smooth surface would lead to lower absorption rates due to reduced surface area.
- **Statement B**: "Digestion would not be as effective because there would be fewer cells to secrete trypsin." This is incorrect as trypsin is secreted by the pancreas, not by the small intestine.
- **Statement C**: "Humans would have needed to evolve a much longer small intestine to absorb sufficient nutrients from their food." This is correct because without the increased surface area from folds and villi, a longer intestine would be necessary to compensate for the reduced absorption efficiency.
- **Statement D**: "Humans would not be able to survive because the digestive tract would be more susceptible to damage." This is incorrect as the smooth surface does not inherently make the digestive tract more susceptible to damage.

6. **Conclusion**: The correct statement is **Statement C**: "Humans would have needed to evolve a much longer small intestine to absorb sufficient nutrients from their food."