How did eukaryotic cells evolve prokaryotic cells?

The hypothesis that eukaryotic cells evolved from a symbiotic association of prokaryotes (endosymbiosis) is particularly well supported by studies of mitochondria and chloroplasts, which are thought to have evolved from bacteria living in large cells.

Explanation:

Both mitochondria and chloroplasts are similar to bacteria in size, and like bacteria, they reproduce by dividing in two.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.