Excretion involves process in which
(a) Harmful substances are stored in cells before being eliminated
(b) Urine is forced out from urinary bladder and sweat from the skin
(c) Harmful substances in the body are chemically changed
(d) Substances of no further use or those present in excessive quantities are thrown out of the body

Options

A. Harmful substances are stored in cells before being eliminated
B. Urine is forced out from urinary bladder and sweat from the skin
C. Harmful substances in the body are chemically changed
D. Substances of no further use or those present in excessive quantities are thrown out of the body

Answer

To solve the question regarding the process of excretion, let's analyze each option step by step:

### Step-by-Step Solution:

1. **Understanding Excretion**:
- Excretion is the biological process through which organisms remove waste products from their bodies. This typically includes the elimination of nitrogenous wastes that result from the metabolism of proteins and nucleic acids.

2. **Analyzing Option (a)**:
- The statement "Harmful substances are stored in cells before being eliminated" suggests that harmful substances are kept in the body. This is incorrect because storing harmful substances can lead to toxicity. Excretion aims to remove these substances rather than store them.

3. **Analyzing Option (b)**:
- The statement "Urine is forced out from urinary bladder and sweat from the skin" describes part of the excretion process but does not encompass the entire mechanism. Excretion involves more than just the act of expelling waste; it includes the conversion and processing of waste materials.

4. **Analyzing Option (c)**:
- The statement "Harmful substances in the body are chemically changed" indicates that excretion involves changing harmful substances. While some substances may be converted into less harmful forms (like urea from ammonia), excretion primarily focuses on the removal of waste rather than just chemical alteration.

5. **Analyzing Option (d)**:
- The statement "Substances of no further use or those present in excessive quantities are thrown out of the body" accurately describes the purpose of excretion. It emphasizes the removal of waste products and excess substances, which aligns with the definition of excretion.

6. **Conclusion**:
- After analyzing all options, option (d) is the most accurate description of the excretion process. It correctly reflects the function of excretion in removing unnecessary or harmful substances from the body.

### Final Answer:
**(d) Substances of no further use or those present in excessive quantities are thrown out of the body.**

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