Monerans that do not have cell wall and smaller known organisms are

Options

A. Methanogens
B. Archaebaceteria
C. Mycoplasına
D. Cyanobacteria

Answer

### Step-by-Step Solution:

1. **Understanding Monerans**: Monerans belong to the kingdom of unicellular prokaryotes. Prokaryotes are organisms whose cells lack a membrane-bound nucleus and other organelles.

2. **Identifying Characteristics**: The question specifically asks for Monerans that do not have a cell wall. Most bacteria have a cell wall made of peptidoglycan, but some exceptions exist.

3. **Examining Options**:
- **Methanogens**: These are a type of Archaebacteria that produce methane. They typically have a cell wall made of pseudopeptidoglycan, which means they do have a cell wall, so they do not fit the criteria.
- **Archaeobacteria**: Similar to methanogens, they also have a cell wall made of pseudopeptidoglycan, thus they do not qualify as Monerans without a cell wall.
- **Mycoplasma**: This genus of bacteria is unique because it lacks a cell wall entirely. This absence of a cell wall makes them resistant to antibiotics like penicillin, which target cell wall synthesis.
- **Cyanobacteria**: Also known as blue-green algae, these organisms have a cell wall made of peptidoglycan, so they do not meet the criteria.

4. **Conclusion**: The only Monerans that do not have a cell wall and are among the smallest known organisms are **Mycoplasma**. Thus, the correct answer is option 3.

### Final Answer:
**Mycoplasma** are the Monerans that do not have a cell wall and are the smallest known organisms.

---