Epithelial cells involved in absorption of digested food have on their free surface.

Options

A. pinocytic vesicles
B. phagocytic vesicles
C. zymogen granules
D. microvilli

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the structures present on the free surface of epithelial cells involved in the absorption of digested food.

2. **Identifying the Options**: The options provided include:
- A) Pinocytic vesicles
- B) Phagocytic vesicles
- C) Zymogen granules
- D) Microvilli

3. **Analyzing Each Option**:
- **Option A (Pinocytic vesicles)**: These are formed during the process of pinocytosis, which is the uptake of liquid nutrients. However, they are not structures found on the free surface of epithelial cells.
- **Option B (Phagocytic vesicles)**: These are involved in the uptake of solid particles through phagocytosis. Similar to pinocytic vesicles, they are not present on the free surface of the cells.
- **Option C (Zymogen granules)**: These are enzyme storage granules found within cells, but they do not pertain to the absorption process directly.
- **Option D (Microvilli)**: These are tiny, finger-like projections on the surface of epithelial cells, particularly in the small intestine. They significantly increase the surface area for absorption.

4. **Conclusion**: The correct answer is **D) Microvilli**. These structures enhance the absorptive capacity of epithelial cells by increasing the surface area available for nutrient absorption.

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