Which of the following is the primary absorptive process in the large intestine?

Options

A. Active transport of `Na^(+)` from the lumen to the blood
B. Absortion of amino acids and fructose
C. Active transport of potassium from the lumen to the blood
D. Active absorption of `HCO_(3)^(-)` into the blood

Explanation

To solve the question "Which of the following is the primary absorptive process in the large intestine?", we will analyze the options provided and understand the primary functions of the large intestine.

### Step-by-Step Solution:

1. **Understand the Role of the Large Intestine**: The large intestine primarily functions in the absorption of water and electrolytes, particularly sodium and chloride ions, from the indigestible food matter.

2. **Evaluate the Options**:
- **Active transport of sodium ion from the lumen to the blood**: This process is significant in the large intestine as it helps in the absorption of sodium, which is crucial for maintaining electrolyte balance.
- **Absorption of amino acids and fructose**: This is primarily a function of the small intestine, where most amino acids and sugars are absorbed.
- **Active transport of potassium from the lumen to the blood**: While potassium is absorbed in the large intestine, it is not the primary absorptive process compared to sodium.
- **Active absorption of bicarbonate ions into the blood**: This process does occur but is not the primary function of the large intestine.

3. **Identify the Primary Process**: The large intestine's mucosa has a high capability for the active absorption of sodium ions. The absorption of sodium creates an electric potential gradient that facilitates the absorption of chloride ions as well.

4. **Role of Aldosterone**: The presence of aldosterone enhances the transport capability of sodium in the large intestine, especially during dehydration, which further emphasizes the importance of sodium absorption.

5. **Conclusion**: Based on the analysis, the primary absorptive process in the large intestine is the **active transport of sodium ions from the lumen to the blood**.

### Final Answer:
The primary absorptive process in the large intestine is the **active transport of sodium ions from the lumen to the blood**.

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