Most living organisms cannot survive at temperature above `45^@`C. How are some microbes able to live in habitats with temperature exceeding `100^@`C?

Options

A. Occurrence of branched chains of lipids reducing fluidity of cell membrane
B. Reduction in amount of free water
C. Development of heat tolerant enzymes
D. All

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks why some microbes can survive in extremely high temperatures (above 100°C) when most living organisms cannot survive above 45°C.

2. **Identifying the Microbes**: The microbes that can survive in such extreme conditions are known as thermophiles. These are a type of archaebacteria specifically adapted to high-temperature environments.

3. **Characteristics of Thermophiles**:
- Thermophiles possess unique adaptations that allow them to thrive in high temperatures.
- One of the key adaptations is the presence of specialized enzymes that remain stable and functional at elevated temperatures. These enzymes are often referred to as heat-tolerant enzymes.

4. **Cell Membrane Composition**:
- The cell membranes of thermophiles contain branched-chain lipids, which differ from the straight-chain lipids found in many other organisms.
- The branched-chain structure helps to reduce membrane fluidity at high temperatures, maintaining the integrity of the cell membrane.

5. **Water Management**:
- Thermophiles also have mechanisms to manage the amount of free water within their cells, which is crucial for maintaining cellular functions under extreme heat.

6. **Conclusion**:
- The ability of thermophiles to survive in temperatures exceeding 100°C is due to a combination of heat-tolerant enzymes, unique lipid compositions in their cell membranes, and effective water management strategies.
- Therefore, the correct answer to the question is that all of the mentioned factors contribute to their survival.

**Final Answer**: All of the above factors (branched chain of lipid, reducing fluidity of cell membrane, production of heat-tolerant enzymes) enable some microbes to survive at temperatures exceeding 100°C.

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