If you’re going hiking this weekend and you have the option of hiking a mountain (A) that is 1400 meters in height and a mountain (B) that is 650 meters in height, BUT you know that you have limited time because of other plans – which mountain would you choose to hike? Why?

The higher you go up the less oxygen there is 

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.