Which of the following statements is not true ?

Options

A. Loop of Henle is largely responsible for concentrated urine
B. Descending limb of loop of Henle is impermeable to solutes
C. Distal convoluted tubule functions in `K^(+)-Na^(+)` homeostasis
D. Descending limb of loop of Henle is impermeable to water

Answer

To determine which statement is not true regarding the excretory system, particularly focusing on the loop of Henle and its functions, we can analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "Loop of Henle is largely responsible for concentrated urine."
- The loop of Henle plays a crucial role in concentrating urine by reabsorbing sodium and potassium ions, as well as water. This statement is true.

2. **Statement 2**: "Decreasing limb of loop of Henle is impermeable to solute."
- The descending limb of the loop of Henle is indeed impermeable to solutes but is permeable to water. This statement is true as it correctly describes the properties of the descending limb.

3. **Statement 3**: "Distal convoluted tubule functions in potassium and sodium homeostasis."
- The distal convoluted tubule (DCT) is involved in the regulation of potassium and sodium levels in the body, and it plays a role in maintaining electrolyte balance. This statement is true.

4. **Statement 4**: "Descending limb of loop of Henle is impermeable to water."
- This statement is incorrect. The descending limb of the loop of Henle is permeable to water, allowing water to be reabsorbed into the surrounding medullary interstitium. The ascending limb, on the other hand, is impermeable to water.

### Conclusion:
The statement that is not true is: **"Descending limb of loop of Henle is impermeable to water."**