Many people might not see an obvious link between cellular respiration and the combustion of gasoline. After all, internal combustion involves the ignition of a volatile fluid. However, combustion and respiration are remarkably similar in that in both contexts one fuel source is broken down in a way that releases its energy in a form that is usable.
Just as an automobile burns gasoline so it can move, living cells burn fuel to provide energy to the body. Instead of burning octane, however, biological organisms do this by oxidizing food, such as sugars, fats and proteins. For example, automobiles burn fuel in this way: octane + oxygen = water + carbon dioxide + energy, while organisms process food like this: sugar + oxygen = carbon dioxide + energy.