In distal convoluted tubule of the nephrons

Options

A. `Na^(+)` reabsorption requires energy
B. `K^(+)` reabsorption does not requires energy
C. Ammonia is excreted
D. Water reabsorption requires energy

Answer

### Step-by-Step Solution:

1. **Understanding the Distal Convoluted Tubule (DCT)**:
- The DCT is a part of the nephron in the kidney that plays a crucial role in the reabsorption of various substances from the filtrate back into the blood.

2. **Analyzing Sodium Reabsorption**:
- Sodium ions (Na+) are reabsorbed in the DCT. This process is primarily active, meaning it requires energy (ATP) to transport sodium against its concentration gradient.
- Approximately 5% of the sodium ions filtered by the kidneys are reabsorbed in the DCT.

3. **Evaluating Potassium Reabsorption**:
- Potassium ions (K+) are also involved in the processes occurring in the DCT. However, potassium is actively secreted into the tubular fluid from the blood, which requires energy.
- Therefore, the statement that potassium reabsorption does not require energy is incorrect.

4. **Examining Ammonia Excretion**:
- Ammonia (NH3) is not excreted in the DCT; instead, it is secreted into the tubular fluid through a diffusion process. This means that ammonia is not actively transported but rather moves passively.

5. **Water Reabsorption in the DCT**:
- Water reabsorption in the DCT occurs mainly through osmosis, which is a passive process and does not require energy. The reabsorption of water can be influenced by the antidiuretic hormone (ADH), but it does not require direct energy input.

6. **Conclusion**:
- Based on the analysis, the only correct statement regarding the DCT is that sodium reabsorption requires energy. The other statements regarding potassium, ammonia, and water reabsorption are incorrect.

### Final Answer:
The correct statement about the distal convoluted tubule of the nephrons is: **Sodium reabsorption requires energy.**

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