Mitochondria and chloroplast are considered to be endosymbionts of cells because they

Options

A. Donot raise de novo
B. Posses their own nucleic acids
C. Have membranes similar to those of bacteria
D. All the above

Answer

To answer the question "Mitochondria and chloroplast are considered to be endosymbionts of cells because they", we will analyze the options provided and understand the reasoning behind the endosymbiotic theory.

### Step-by-Step Solution:

1. **Understanding Endosymbionts**:
- Endosymbionts are organisms that live within the body or cells of another organism in a mutually beneficial relationship. In this context, mitochondria and chloroplasts are considered endosymbionts because they were once free-living prokaryotic organisms that became incorporated into eukaryotic cells.

2. **Analyzing the Options**:
- **Option A: Do not raise de novo**: This option suggests that mitochondria and chloroplasts do not arise from scratch or de novo. While they do not arise de novo, this statement alone does not fully explain why they are considered endosymbionts.
- **Option B: Possess their own nucleic acid**: This is a significant point. Mitochondria and chloroplasts contain their own DNA, which is similar to bacterial DNA. This characteristic supports the idea that they originated from free-living bacteria.
- **Option C: Have membranes similar to those of bacteria**: Both mitochondria and chloroplasts have double membranes, and their inner membranes are similar to the membranes found in bacteria. This is another piece of evidence supporting the endosymbiotic theory.
- **Option D: All of the above**: This option suggests that all the previous statements are true.

3. **Conclusion**:
- While options B and C provide strong evidence for the endosymbiotic theory, option D encompasses all the relevant points. However, the most direct answer to the question about why they are considered endosymbionts focuses on their possession of their own nucleic acid.
- Therefore, the best answer is **Option B: possesses their own nucleic acid**.

### Final Answer:
Mitochondria and chloroplasts are considered to be endosymbionts of cells because they **possess their own nucleic acid**.

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