"Bacterial Endosymbionts and Chloroplasts" (theory)

Bacterial endosymbionts are bacteria that live inside other organisms, forming a mutually beneficial relationship. The theory of chloroplast origin suggests that ancient photosynthetic bacteria were engulfed by early plant ancestors, becoming permanent parts of their cells. These bacteria evolved into chloroplasts—the structures responsible for photosynthesis, which allows plants to convert sunlight into energy. This symbiotic relationship explains how chloroplasts originated from free-living bacteria that became integrated into plant cells billions of years ago, forming a critical part of plant biology and the development of life on Earth.