The organisms which completely lack a cell wall and can live without oxygen are

Options

A. Mycoplasmas
B. Archaebacteria
C. Methanogens
D. Thermoacidophiles

Answer

To answer the question about organisms that completely lack a cell wall and can live without oxygen, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics of the Organisms**:
- We need to find organisms that have two specific characteristics:
1. They completely lack a cell wall.
2. They can survive in the absence of oxygen (anaerobic conditions).

2. **Consider the Options**:
- The options provided are: Mycoplasma, Archaea, Methanogens, and Thermoacidophiles.
- We will analyze each option based on the characteristics identified in step 1.

3. **Analyze Mycoplasma**:
- Mycoplasma are known to be prokaryotic organisms that do not have a cell wall.
- They are also capable of surviving without oxygen, making them anaerobic.

4. **Analyze Archaea**:
- Archaea is a broad category that includes various types of organisms, some of which can lack a cell wall (like certain Methanogens).
- However, not all Archaea lack a cell wall, so we need to be more specific.

5. **Analyze Methanogens**:
- Methanogens are a type of Archaea that produce methane and are known to thrive in anaerobic environments.
- Some Methanogens do lack a cell wall, making them fit the criteria.

6. **Analyze Thermoacidophiles**:
- Thermoacidophiles are also a type of Archaea that thrive in extreme conditions (high temperature and acidity).
- They typically have a cell wall, so they do not fit the criteria.

7. **Conclusion**:
- Based on the analysis, Mycoplasma and certain Methanogens fit the criteria of organisms that completely lack a cell wall and can live without oxygen.
- However, since Mycoplasma is specifically known for lacking a cell wall and being anaerobic, it is the most fitting answer.

### Final Answer:
The organisms which completely lack a cell wall and can live without oxygen are **Mycoplasma**.