Which statement is wrong?

Options

A. The counter current mechanism changes the isotonic glomerular filtrate into hypertonic urine by increasing salt concentration around the nephron and collecting tubule.
B. The wall of collecting tubule is permeable to water whereas ascending limb is impermeable to water.
C. The absorption of water in DCT is facultative
D. As the filtrate passes through the ascending limb, sodium is transported passively in ascending thick segment.

Answer

To determine which statement is wrong regarding the excretory system and nephron function, we will evaluate each statement provided.

### Step-by-Step Solution:

1. **Evaluate Statement 1**:
- Statement: "The counter current mechanism changes the isotonic glomerular filtrate into hypertonic urine by increasing salt concentration around the nephron and collecting tube."
- Analysis: The counter-current mechanism does indeed concentrate urine by creating a hypertonic environment in the medulla, allowing for water reabsorption. This statement is **true**.

2. **Evaluate Statement 2**:
- Statement: "The wall of collecting tubule is permeable to water whereas ascending limb is impermeable to water."
- Analysis: The collecting duct is permeable to water (especially under the influence of ADH), while the ascending limb of the loop of Henle is indeed impermeable to water. This statement is **true**.

3. **Evaluate Statement 3**:
- Statement: "The absorption of water in DCT is facultative."
- Analysis: The distal convoluted tubule (DCT) does have the ability to reabsorb water, but this process is regulated and can be adjusted based on the body’s needs, making it facultative. This statement is **true**.

4. **Evaluate Statement 4**:
- Statement: "As the filtrate passes through the ascending limb, sodium is transported passively in ascending thick segment."
- Analysis: Sodium is actively transported out of the ascending limb of the loop of Henle, not passively. Therefore, this statement is **false**.

### Conclusion:
The wrong statement among the provided options is **Statement 4**: "As the filtrate passes through the ascending limb, sodium is transported passively in ascending thick segment."

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