Which is true of excretion

Options

A. Large amount of water from renal filtrate is absorbed by DCT and lesser amount in PCT
B. Descending limb of loop of Henle is impermeable to salts
C. Malpighian corpuscles occur in renal medulla
D. Urine is pale yellow and slightly alkaline

Answer

**Step-by-Step Solution:**

1. **Understanding Excretion**: Excretion is the process of eliminating waste products from the body. It is crucial for maintaining homeostasis and involves various organs, primarily the kidneys.

2. **Analyzing the Statements**: The question provides four statements regarding excretion. We need to evaluate each statement to determine which one is true.

3. **Evaluating Statement 1**:
- Statement: "Large amount of water from the renal filtrate is absorbed by the DCT and lesser amount in the PCT."
- Evaluation: This statement is incorrect. The proximal convoluted tubule (PCT) is responsible for the reabsorption of approximately 70-80% of water and electrolytes, while the distal convoluted tubule (DCT) absorbs a lesser amount of water, primarily under hormonal control.

4. **Evaluating Statement 2**:
- Statement: "Descending limb of Loop of Henle is impermeable to salt."
- Evaluation: This statement is correct. The descending limb of the Loop of Henle is permeable to water but not to salts, making this the true statement.

5. **Evaluating Statement 3**:
- Statement: "Malpighian corpuscle occurs in the renal medulla."
- Evaluation: This statement is incorrect. The Malpighian corpuscle, which consists of Bowman's capsule and the glomerulus, is located in the renal cortex, not the medulla.

6. **Evaluating Statement 4**:
- Statement: "Urine is pale yellow, slightly alkaline."
- Evaluation: This statement is partially correct. While urine is indeed pale yellow due to the pigment urochrome, it is slightly acidic (with a pH around 6.8), not alkaline. Therefore, this statement is also incorrect.

7. **Conclusion**: After evaluating all statements, only Statement 2 is true. Thus, the correct answer is that the descending limb of the Loop of Henle is impermeable to salt.

**Final Answer**: The true statement about excretion is that the descending limb of the Loop of Henle is impermeable to salt.

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