During the first part, during sunlight that is, pyruvatric acid is augmented during proton formation. This is where oxygen is formed at a rate of 150 ppm. During darkness, the carbon is oxidized and allowed to build up, which will ultimately produce more water (which is important for plants and other photosynthesizing organisms) and power the processes that make fructose and sucrose (ie: sugars). Over extended periods of darkness, this build up of sugar is able to keep the plant from deteriorating and can help it go dormant (kind of like hibernating) until conditions improve.
