(I) In order for us to survive, our bodies have figured out various ways to extract energy from our surroundings. (II) One of the ways is with food, which provides our cells with raw materials to make repair and replace our cells as needed. (III) As soon as the oxygen enters your blood, a passing protein molecule called hemoglobin picks it up. (IV) A different kind of energy we need is that which allows us to make use of these raw materials. (V) The body has figured out a way to extract this from oxygen.