Which of the following is a characteristic of mitochondria and chloroplasts that supports the endosymbiotic theory?

Question

BlackTom AI · Accepted Answer

Both mitochondria and chloroplasts contain their own circular DNA molecules, a hallmark supporting their origin as formerly free-living prokaryotes.

1. Relevant knowledge points and concepts
- Endosymbiotic theory: mitochondria and chloroplasts originated from ancestral free-living bacteria that entered into a symbiotic relationship with a host cell.
- Supporting evidence includes: presence of their own DNA (often circular), prokaryote-like 70S ribosomes, double membranes, ability to divide by binary fission, and synthesis of some of their own proteins.
- Distinctions between organelle features and eukaryotic cytoplasmic features (e.g., 70S vs 80S ribosomes).

2. Step-by-step reasoning
- Check each answer choice against known evidence for endosymbiosis.
- Determine which characteristic(s) are true for both organelles and are considered evidence of prokaryotic origin.

3. Intermediate steps / facts used
- Mitochondria contain mitochondrial DNA (mtDNA), usually circular and encoding some mitochondrial proteins and RNAs.
- Chloroplasts contain chloroplast DNA (cpDNA), also circular, encoding some photosynthetic proteins and RNAs.
- Both organelles replicate by a process similar to binary fission and have ribosomes that resemble bacterial 70S ribosomes (not identical to eukaryotic 80S).

4. Why the correct answer is correct
- "Both contain DNA molecules": True. The presence of their own genomes (circular DNA molecules) indicates they retained genetic material from ancestral prokaryotes, a central pillar of the endosymbiotic theory. This directly supports descent from free-living bacteria capable of encoding essential organelle components.

5. Why other options are incorrect
- "Both contain endoplasmic reticulum and Golgi bodies.": False; those are separate eukaryotic organelles, not components of mitochondria or chloroplasts.
- "Both have bacteria-like polysaccharide cell walls.": False; mitochondria and chloroplasts do not possess bacterial cell walls surrounding them inside eukaryotic cells.
- "Both contain ribosomes that are identical to ribosomes of the eukaryotic cytoplasm.": False; their ribosomes are prokaryote-like (70S), not identical to eukaryotic 80S ribosomes.
- "Both can reproduce on their own outside of the cell.": False; they divide within host cells and cannot independently live and reproduce outside the cellular environment.

6. Conclusion confirming the answer
- Therefore, the correct choice is: Both contain DNA molecules. This matches the provided answer.

Which of the following is a characteristic of mitochondria and chloroplasts that supports the endosymbiotic theory?单项选择题

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