What is true for Archaebacteria

Options

A. All are halophiles
B. All are photosynthetic
C. All are fossils
D. Oldest living beings

Answer

### Step-by-Step Solution:

1. **Understanding Archaebacteria**:
- Archaebacteria are a group of microorganisms that are distinct from bacteria and eukaryotes. They are known for their ability to survive in extreme environments.

2. **Evaluating the Statements**:
- The question provides four statements about Archaebacteria:
1. All are halophiles.
2. All are photosynthetic.
3. All are fossils or oldest living beings.
4. All are extremophiles.

3. **Analyzing Each Statement**:
- **Statement 1: All are halophiles**:
- This is incorrect. Halophiles are a specific type of Archaebacteria that thrive in high-salt environments, but not all Archaebacteria fall into this category.
- **Statement 2: All are photosynthetic**:
- This is also incorrect. While some Archaebacteria can perform photosynthesis, many are heterotrophic, meaning they rely on other organisms for their nutrients.
- **Statement 3: All are fossils**:
- This statement is misleading. While Archaebacteria are often referred to as "living fossils" due to their ancient origins, they are not all fossils; many still exist today.
- **Statement 4: Oldest living beings**:
- This statement is true. Archaebacteria are among the oldest forms of life on Earth, having existed for billions of years.

4. **Conclusion**:
- The correct statement regarding Archaebacteria is that they are the "oldest living beings." This reflects their long evolutionary history and continued existence in various environments.

### Final Answer:
- The true statement for Archaebacteria is: **They are the oldest living beings.**