Monerans with chlorophyll 'a' and oxygenic photosynthesis are

Options

A. Actinomycetes
B. Mycoplasma
C. Bacteria
D. Cyanobacteria

Answer

### Step-by-Step Solution:

1. **Understanding Monerans**: Monerans are a group of prokaryotic organisms that include bacteria and blue-green algae (cyanobacteria). They are characterized by the absence of a defined nucleus.

2. **Identifying Chlorophyll 'a'**: Chlorophyll 'a' is a pigment found in various photosynthetic organisms, including plants and certain types of bacteria. It plays a crucial role in the process of photosynthesis.

3. **Defining Oxygenic Photosynthesis**: Oxygenic photosynthesis is a process where organisms use light energy to convert carbon dioxide and water into glucose and oxygen. This process is characteristic of plants, algae, and certain bacteria.

4. **Linking Chlorophyll 'a' and Oxygenic Photosynthesis**: Among monerans, the organisms that possess chlorophyll 'a' and are capable of oxygenic photosynthesis are specifically blue-green algae.

5. **Identifying the Correct Group**: Blue-green algae are also known as cyanobacteria. They are the only group of monerans that can perform oxygenic photosynthesis due to the presence of chlorophyll 'a'.

6. **Eliminating Incorrect Options**: Other monerans like actinomycetes, mycoplasma, and certain bacteria do not perform oxygenic photosynthesis, thus they cannot be the answer.

7. **Conclusion**: Therefore, the correct answer to the question is that monerans with chlorophyll 'a' and capable of oxygenic photosynthesis are known as **cyanobacteria**.

### Final Answer:
Cyanobacteria