The most primitive organisms showing oxygenic photosynthesis are

Options

A. Green algae
B. Chrysophytes
C. Green and purple sulphur bacteria
D. Cyanobacteria

Answer

**Step-by-Step Solution:**

1. **Understand Oxygenic Photosynthesis**:
- Oxygenic photosynthesis is the process by which certain organisms convert light energy into chemical energy, releasing oxygen as a by-product. This distinguishes it from anoxygenic photosynthesis, where oxygen is not produced.

2. **Identify the Organisms**:
- The question asks for the most primitive organisms that perform oxygenic photosynthesis. Primitive organisms are typically prokaryotic, meaning they lack membrane-bound organelles.

3. **Consider the Types of Organisms**:
- Bacteria are the most primitive organisms, and they can be categorized into different types based on their photosynthetic capabilities.
- Green algae and chrysophytes (golden algae) are eukaryotic and belong to the kingdom Protista, so they are not considered primitive in this context.

4. **Evaluate the Options**:
- Green algae: Eukaryotic, thus not primitive.
- Chrysophytes: Also eukaryotic, thus not primitive.
- Green and purple sulfur bacteria: These perform anoxygenic photosynthesis, so they do not fit the criteria.
- Cyanobacteria (blue-green algae): These are prokaryotic and perform oxygenic photosynthesis.

5. **Conclusion**:
- The most primitive organisms that show oxygenic photosynthesis are cyanobacteria, also known as blue-green algae. Therefore, the correct answer is cyanobacteria.

**Final Answer**: Cyanobacteria (blue-green algae).

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