Which of the following is the most ancient organism having oxygenic photosynthesis?

Options

A. cholorobium
B. anabaena
C. mycoplasma
D. halophiles

Answer

To solve the question "Which of the following is the most ancient organism having oxygenic photosynthesis?" we will analyze the provided options step by step.

### Step 1: Understand the Options
The options given are:
1. Chlorobium
2. Anabena
3. Mycoplasma
4. Halophiles

### Step 2: Identify the Type of Photosynthesis
We need to determine which of these organisms performs oxygenic photosynthesis, which is the process of photosynthesis that produces oxygen as a byproduct.

- **Chlorobium**: This organism is known for performing anoxygenic photosynthesis, which does not produce oxygen.
- **Anabena**: This organism is a type of cyanobacteria that is known to perform oxygenic photosynthesis, producing oxygen as a byproduct.
- **Mycoplasma**: This organism is anaerobic and does not perform photosynthesis, so it cannot be considered for oxygenic photosynthesis.
- **Halophiles**: These organisms thrive in saline environments and do not perform oxygenic photosynthesis.

### Step 3: Determine the Most Ancient Organism
Among the organisms that perform oxygenic photosynthesis, we need to identify which one is the most ancient.

- **Anabena** (cyanobacteria) is recognized as one of the earliest organisms capable of oxygenic photosynthesis, contributing significantly to the Earth's atmosphere by producing oxygen.

### Conclusion
Based on the analysis above, the most ancient organism having oxygenic photosynthesis is **Anabena**.

### Final Answer
**Anabena**

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