Answer: The organelles that were engulfed have a double membrane.
Explanation:
The endosymbiotic theory suggests that mitochondria and chloroplasts are the organelles that are present in the eukaryotic cells that have been evolved from the prokaryotic cells typically of primitive bacteria. The bacteria or primitive prokaryotic cell must have a single membrane the eukaryotic cell organelle which engulfed it later became the double membrane structure. These organelles have their own DNA just like individual prokaryotic cell and their DNA is circular in shape just like individual prokaryotic cell.