Final answer:
Mitochondria and chloroplasts originated in the first eukaryotic cells through endosymbiotic relationships with prokaryotes. Mitochondria evolved before chloroplasts, as all eukaryotes have functional mitochondria but plastids are only found in certain eukaryotes. Endosymbiosis led to the incorporation of these organelles into ancestral eukaryotic cells.
Step-by-step explanation:
According to the Endosymbiotic Theory, the first eukaryotic cells may have originated from ancestral prokaryotes that underwent membrane proliferation, compartmentalization of cellular function, and established endosymbiotic relationships with aerobic prokaryotes (for mitochondria) and photosynthetic prokaryotes (for chloroplasts). Mitochondria likely originated before chloroplasts because all eukaryotes have functional mitochondria, whereas plastids are only found in certain eukaryotes like plants and algae. The process of endosymbiosis resulted in the incorporation of these organelles into the ancestral eukaryotic cells, providing them with energy production and photosynthetic capabilities respectively.