Why everything needs oxygen to stay alive in the world?

Question

I knew the answer but it just slip out of my mind so why does everything needs oxygen to stay alive and carry out chemical reactions ,as a hint from what i remembered that O2 a oxygen molecule's elctrons has to do something ,Give An Example Too

Answer 1

Oxygen is combustible. It burns the food we take into energy. Energy is needed even to sleep! So without oxygen ther's no energy and without energy no work can be done.

Answer 2

What about plants?