Ribosomes that occur exclusively in mitochondria are

Options

A. 70 S
B. 55 S
C. 30 S
D. 50 S

Answer

To solve the question regarding the type of ribosomes that occur exclusively in mitochondria, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Ribosome Structure**: Ribosomes are made up of two subunits: a smaller subunit and a larger subunit. The size of these subunits is measured in Svedberg units (S).

2. **Identify Mitochondrial Ribosomes**: Mitochondria have their own ribosomes, which are similar to prokaryotic ribosomes. In general, mitochondrial ribosomes are classified as 70S ribosomes.

3. **Review the Options Given**: The options provided are:
- A) 70S
- B) 55S
- C) 30S
- D) 50S

4. **Analyze Each Option**:
- **70S**: This is the correct classification for mitochondrial ribosomes, as they are similar to those found in prokaryotes.
- **55S**: This is not a standard classification for mitochondrial ribosomes.
- **30S**: This is typically associated with the smaller subunit of prokaryotic ribosomes.
- **50S**: This refers to the larger subunit of prokaryotic ribosomes.

5. **Conclusion**: Based on the analysis, the ribosomes that occur exclusively in mitochondria are classified as **70S**.

### Final Answer:
**A) 70S**