Final answer:
Chloroplasts are the organelles that originated from photosynthetic bacteria through an endosymbiotic event. This is part of the endosymbiotic theory, which explains how mitochondria and chloroplasts evolved from aerobic and photosynthetic bacteria, developing a symbiotic relationship within eukaryotic host cells.
Step-by-step explanation:
The organelle that brought about photosynthetic bacteria through an endosymbiotic event is known as the chloroplast. This process stems from a historical biological event where an early eukaryote engulfed a photosynthetic bacterium. Instead of digesting it, the bacterium lived symbiotically within the host cell, eventually evolving into the chloroplasts we see today in plants and some algae.
According to endosymbiotic theory, proposed by Lynn Margulis, mitochondria and chloroplasts, which have their own DNA that resembles that of prokaryotes, indicate that these organelles originated from ancient symbiotic bacteria. Scientists believe mitochondria evolved from aerobic bacteria, while chloroplasts came from photosynthetic bacteria, specifically cyanobacteria, leading to a mutually beneficial relationship over millions of years.
The endosymbiosis involved gram-negative bacteria, which can be deduced from the double membrane characteristic of both mitochondria and chloroplasts. This process is deemed a second symbiotic event following the initial event where a bacterial ancestor became a mitochondrion in host eukaryotic cells.