Final answer:
The Endosymbiosis Theory explains how mitochondria and chloroplasts became organelles in a eukaryotic cell.
Step-by-step explanation:
The theory that helps explain how mitochondria and chloroplasts became organelles outside of the system of connected membranes in a eukaryotic cell is known as the Endosymbiosis Theory. According to this theory, mitochondria and chloroplasts were once independent prokaryotic organisms that were engulfed by early eukaryotic cells and formed a symbiotic relationship with them. This theory is supported by various pieces of evidence, such as the presence of DNA within mitochondria and chloroplasts, their ability to divide independently, and their similarity to free-living prokaryotes in terms of structure and function.
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