Final answer:
The endosymbiotic theory explains how eukaryotic cells evolved from a symbiotic relationship between specialized prokaryotes and ancestral cells. Mitochondria evolved to perform specialized cellular functions before chloroplasts were incorporated into eukaryotic cells.
Step-by-step explanation:
The endosymbiotic theory explains how eukaryotic cells evolved from a symbiotic relationship between prokaryotic cells. Some prokaryotes, such as aerobic bacteria, adapted to perform specialized cellular functions. They evolved into mitochondria, specialized for breaking down chemicals and releasing energy.
Other prokaryotes, like cyanobacteria, specialized in photosynthesis and evolved into chloroplasts. The incorporation of mitochondria into ancestral eukaryotic cells occurred before the incorporation of chloroplasts.