Which feature supports endosymbiotic theory for mitochondria and chloroplasts?

Which feature supports endosymbiotic theory for mitochondria and chloroplasts?

• A. Linear DNA and single membranes.
• B. Circular DNA with bacteria-like ribosomes.
• C. Chromosomes associated with host nucleus.
• D. No division independent of the cell.

Answer: (B)

The key idea is that mitochondria and chloroplasts carry evidence of a bacterial origin. Circular DNA is typical of many bacteria, not the linear chromosomes of the host cell, and the ribosomes inside these organelles are more like bacterial ribosomes (70S) than the host’s eukaryotic 80S ribosomes. This combination—circular DNA with bacteria-like ribosomes—strongly supports the idea that these organelles began as free-living bacteria that were internalized by an ancestral cell and retained their own genetic material and protein-making machinery. In addition, these organelles have double membranes and can replicate by division within the cell, which fits the bacterial-like inheritance pattern and reinforces the endosymbiotic view.

The key idea is that mitochondria and chloroplasts carry evidence of a bacterial origin. Circular DNA is typical of many bacteria, not the linear chromosomes of the host cell, and the ribosomes inside these organelles are more like bacterial ribosomes (70S) than the host’s eukaryotic 80S ribosomes. This combination—circular DNA with bacteria-like ribosomes—strongly supports the idea that these organelles began as free-living bacteria that were internalized by an ancestral cell and retained their own genetic material and protein-making machinery. In addition, these organelles have double membranes and can replicate by division within the cell, which fits the bacterial-like inheritance pattern and reinforces the endosymbiotic view.