Endosymbiosis theory explains the origin of chloroplast and mitochondria in the eukaryotic organisms.
When the pro-eukaryotes engulfed the blue-green algae or photosynthetic bacteria, these bacteria formed the symbiotic relationship with the pro-eukaryotes. These photosynthetic bacteria transformed into the chloroplast organelles of the eukaryotes which can capture the sunlight and use it in the synthesis of glucose molecules. These eukaryotic cells later formed the plant kingdom.
