Homeostasis is maintained by

Options

A. Transport system
B. Favourable changes in extracellular fluid
C. Hormonal signals
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding Homeostasis**: Homeostasis refers to the process by which living organisms maintain a stable internal environment despite changes in external conditions. This includes regulation of temperature, pH, and osmotic balance.

2. **Identifying Mechanisms of Homeostasis**:
- **Transport System**: In humans, the transport system primarily consists of the heart and blood. Blood plays a crucial role in transporting nutrients, gases, and waste products throughout the body, which helps in maintaining a stable internal temperature and overall homeostasis.
- **Hormonal Signals**: Hormones are chemical messengers that regulate various physiological processes. They help in maintaining homeostasis by controlling the absorption and excretion of substances, thus influencing internal pH and osmotic concentration.
- **Favorable Changes in Extracellular Fluid**: The extracellular fluid surrounds cells and its composition can affect cellular function. Changes in the concentration of substances in the extracellular fluid can influence the internal environment of the cells, thus contributing to homeostasis.

3. **Conclusion**: Since all three mechanisms (transport system, hormonal signals, and favorable changes in extracellular fluid) play a role in maintaining homeostasis, the correct answer to the question is "all of the above."

4. **Final Answer**: Homeostasis is maintained by **all of the above** (Option 4).

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