Excretion is

Options

A. Removal of substrances not required by body
B. Removal of useless substances and susbtances present in excess
C. Formation of substances having some role in body
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding Excretion**: Excretion is the biological process through which organisms remove waste products from their bodies. It is often confused with the elimination of fecal matter, but it specifically refers to the removal of urine.

2. **Identifying the Components of Urine**: Urine is not just composed of water; it contains various unwanted substances, including excess salts, urea, and other metabolic waste products.

3. **Analyzing the Options**:
- **Option A**: "Removal of substances not required by the body" - This is too broad and can include substances that may not be waste but are still present in the body.
- **Option B**: "Removal of useless substances and the substances present in excess" - This accurately describes excretion, as it involves removing waste and excess materials.
- **Option C**: "Formation of substances having some role in the body" - This is incorrect because excretion does not involve the formation of new substances.
- **Option D**: "All of the above" - Since options A and C are incorrect, this option cannot be correct.

4. **Conclusion**: The most accurate definition of excretion from the provided options is **Option B**: "Removal of useless substances and the substances present in excess."

**Final Answer**: Excretion is the removal of useless substances and the substances present in excess.

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