According to endosymbiosis, what is the best explanation about the eukaryotic cells evolved?

The best explanation about the eukaryotic cell evolved is this: CHLOROPLAST AND MITOCHONDRIA WERE ONCE PROKARYOTES THAT BEGAN TO LIVE WITHIN LARGER CELLS.
Endosymbiosis theory holds that some cell organelles are developed from prokaryotes which once has a symbiosis relationship with eukaryotes but which later become trapped within the cells of these eukaryotes. Examples of these type of cell organelles are chloroplast and mitochondria.

What do you mean about innate behavior i don’t get it

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.