We shall look first in this chapter at the metabolism of glucose: its breakdown without oxygen into smaller molecules, the added improvement of combustion with oxygen (respiration), and then the resynthesis of glucose when energy is not needed. We then shall turn to photosynthesis: the light-trapping reactions that make energy-rich ATP and NADPH molecules, and the "dark reactions" that use these molecules to synthesize glucose. Both of these glucose-making pathways have common features, which suggest a common origin, and these clues will be followed up in Chapter 26.

It cannot be emphasized too strongly that this chapter is not intended to be an exercise in memorization. What we are looking for are the pathways of energy flow that living organisms use to stay alive. It is far less important that you remember how to write the conversion of one molecule into another, than that when you look at the two molecules, you understand what happened between one and the other to liberate energy. If any series of chemical reactions can be said to have a strategy, this is what we are after. Don't memorize the molecules, study the patterns. It is better to appreciate something you can't remember, than to remember something you don't understand.