Which of the following hormones control 24 - hour diurnal cycle or rhythmic activity of human body ?

Options

A. Thymosin
B. Melanin
C. Melatonin
D. Thyroxine

Answer

To solve the question regarding which hormone controls the 24-hour diurnal cycle or rhythmic activity of the human body, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which hormone regulates the 24-hour diurnal cycle in humans. This cycle includes various physiological processes that follow a roughly 24-hour rhythm, such as the sleep-wake cycle.

2. **Analyzing the Options**:
- **Thymosine**: This hormone is primarily involved in immune function. It does not play a role in regulating the diurnal cycle. Therefore, this option is incorrect.
- **Melanin**: This is a pigment responsible for skin color and does not influence the body's rhythmic activities. Thus, this option is also incorrect.
- **Melatonin**: This hormone is produced by the pineal gland and is well-known for its role in regulating sleep-wake cycles and other circadian rhythms. This option is likely correct.
- **Thyroxine (T4)**: This hormone is produced by the thyroid gland and primarily regulates metabolism, not the diurnal cycle. Hence, this option is incorrect.

3. **Identifying the Correct Answer**: Based on the analysis, the hormone that regulates the 24-hour diurnal cycle is **melatonin**.

4. **Conclusion**: Therefore, the correct answer to the question is **melatonin**.

### Final Answer:
**Melatonin** is the hormone that controls the 24-hour diurnal cycle or rhythmic activity of the human body.

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