Which of the following organisms completely lack cell wall, they are the smallest living cells known and can servive without oxygen ?

Options

A. Actinomycetes
B. PPLO
C. Rickettsia
D. Chalmydiae

Answer

To solve the question regarding which organism completely lacks a cell wall, is the smallest living cell known, and can survive without oxygen, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics Required**: The question specifies three characteristics:
- Completely lacks a cell wall
- Smallest living cells known
- Can survive without oxygen

2. **Evaluate the Options**: We need to analyze the given options based on the characteristics mentioned.

3. **Analyze Rickettsia and Chlamydiae**:
- Both are obligate intracellular bacteria.
- They are gram-negative and have a cell wall.
- Rickettsia requires oxygen (aerobic), while Chlamydiae can survive without it (anaerobic).
- **Conclusion**: Both have a cell wall, so they do not meet the criteria.

4. **Analyze Actinomycetes**:
- These are gram-positive bacteria.
- They also possess a cell wall.
- Some are aerobic and some are anaerobic.
- **Conclusion**: They have a cell wall, so they do not meet the criteria.

5. **Analyze Mycoplasma (PPLO)**:
- Mycoplasma, also known as pleuropneumonia-like organisms (PPLO), are known to be the smallest living cells.
- They completely lack a cell wall.
- They are facultative anaerobes, meaning they can survive without oxygen and can also grow in its presence.
- **Conclusion**: Mycoplasma meets all the criteria.

6. **Final Answer**: The organism that completely lacks a cell wall, is the smallest living cell known, and can survive without oxygen is **Mycoplasma (PPLO)**.