Which among the following are the smallest living cells, known without a definite cell wall, pathogenic to plants as well as animals and can survive without oxygen ?

Options

A. Bacillus
B. Pseudomonas
C. Mycoplasma
D. Nostoe

Answer

To solve the question regarding the smallest living cells known without a definite cell wall, pathogenic to plants and animals, and capable of surviving without oxygen, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics Required**:
- The organism must be the smallest living cells.
- It should lack a definite cell wall.
- It must be pathogenic to both plants and animals.
- It should be able to survive without oxygen.

2. **Evaluate the Options**:
- **Bacillus**: This is a genus of bacteria that has a cell wall and is not the smallest living cell. It is pathogenic but does not meet all the criteria.
- **Pseudomonas**: Another genus of bacteria that has a cell wall and is pathogenic, but again, it is not the smallest living cell.
- **Mycoplasma**: This group of bacteria is known to be the smallest living cells. They lack a cell wall, are pathogenic to both plants and animals, and can survive without oxygen. This option meets all the criteria.
- **Nostoc**: This is a cyanobacteria (blue-green algae) that has a cell wall and is not the smallest living cell. It is involved in nitrogen fixation and does not meet the criteria.

3. **Conclusion**:
- After evaluating all the options, the only organism that fits all the criteria is **Mycoplasma**. Therefore, the correct answer is **Mycoplasma**.

### Final Answer:
**Mycoplasma** is the correct answer.

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