Final answer:
The endosymbiotic theory proposes that mitochondria and chloroplasts originated from prokaryotic cells engulfed by early eukaryotic ancestors, which evolved into an interdependent relationship. Strong evidence includes similarities in DNA and reproduction mechanisms to bacteria, and the theory is widely supported by the scientific community.
Step-by-step explanation:
The Endosymbiotic Theory: The proposal that mitochondria and chloroplasts are descendants of early prokaryotic cells that resided and evolved within primitive cells is central to the endosymbiotic theory. This theory explains the origin of these organelles as a result of endosymbiotic events where ancestral eukaryotic cells engulfed aerobic bacteria, leading to mitochondria, and photosynthetic bacteria, developing into chloroplasts. Evidence supporting this includes similarities in biochemistry and DNA between these organelles and prokaryotic cells, the binary fission of these organelles akin to bacterial reproduction, and the presence of double membranes characteristic of prokaryotic cells.
Originally proposed by Lynn Margulis in the 1960s, the endosymbiotic theory suggests that the intricate relationship between the host cell and its internal companions evolved over time, with the internalized bacteria becoming permanent residents, providing essential functions for the host cell. Mitochondria became centers of aerobic respiration, while chloroplasts enabled photosynthesis in plants and some algae. The endosymbiotic theory has since become widely accepted due to substantial genetic and biochemical evidence.