Which of the following are found in extreme saline conditions?

Options

A. Eubacteria
B. Cyanobacteria
C. Mycobacteria
D. Archaebacteria

Answer

To determine which of the following organisms are found in extreme saline conditions, let's analyze the options provided:

1. **U-bacteria**: This term is not commonly used in biological classification. It might refer to a general category of bacteria, but it does not specifically indicate an organism known for thriving in extreme saline conditions.

2. **Cyanobacteria**: These are photosynthetic bacteria that are found in a variety of environments, including freshwater and marine ecosystems. However, they are not specifically known for thriving in extreme saline conditions.

3. **Mycobacteria**: This group includes bacteria that are known for causing diseases such as tuberculosis and leprosy. They are not typically associated with extreme saline environments.

4. **Archaebacteria**: This group, also known as Archaea, includes organisms that are known to thrive in extreme environments, including high salinity, high temperature, and extreme acidity. Specifically, halophiles are a type of Archaea that live in highly saline environments.

Based on this analysis, the correct answer is **D - Archaebacteria**. They are uniquely adapted to survive in extreme saline conditions due to their distinct cell wall structure and metabolic pathways.

### Step-by-Step Solution:
1. **Identify the options**: U-bacteria, Cyanobacteria, Mycobacteria, and Archaebacteria.
2. **Analyze each option**:
- U-bacteria: Not a recognized category for extreme saline conditions.
- Cyanobacteria: Found in various environments but not specifically extreme saline.
- Mycobacteria: Associated with diseases, not extreme saline.
- Archaebacteria: Known for thriving in extreme environments, including saline.
3. **Conclude**: The organism that thrives in extreme saline conditions is Archaebacteria.