This diagram provides an overview of the major redox couples that provide the energy that drives the life process .
Aerobic respiration is the most efficient of all because the electron falls so far.
To make the glucose, animals rely on plants, which utilize the energy of sunlight to force electrons from O 2 back up to the top left of the diagram. This of course is photosynthesis, which is just respiration driven in reverse. Aerobic respiration is a fairly recent development in the history of life. Farther still up the diagram you will see the sulfate ion. This is present in all soils, and its reduction product H 2 S produces the rotten-egg odor that is often noticed in heavy muds into which O 2 is unable to penetrate.