Endosymbiotic theory should begin with two seperate cells, one being a smaller specialized bacteria, and the other being a larger cell.
الانزلاق: 2
Awesome! If you don't mind me asking, why should we consider hiring you?
This larger cell was rather simple. It could swallow things and eat them, but it couldn't use oxygen to efficiently make energy.
الانزلاق: 3
Uhhh...I'm kind of a good at making energy...I guess.
الانزلاق: 4
Great! Your hired! Now to finish the onboarding process, let me engulf you!
Hypothetically, one day, billions of years ago, this larger cell engulfed the bacteria, but instead of being digested, the bacteria survived within the cell.
الانزلاق: 5
Wait, what?
The bacteria helped the larger cell produce energy, both benefiting each other. The larger cell reproduced, and so did the bacteria within them, eventually evolving into the mitochondria.
الانزلاق: 6
Huh. This actually isn't that bad...
Eventually, these new evolved cells swallowed another bacterium, leading to the development of chloroplasts. We have a lot of evidence for this theory, such as the fact mitochondria and chloroplasts have different DNA. They even mutiply by dividing in half, exactly like bacteria do!