<P> Carbohydrates are central to many essential metabolic pathways . Plants synthesize carbohydrates from carbon dioxide and water through photosynthesis, allowing them to store energy absorbed from sunlight internally . When animals and fungi consume plants, they use cellular respiration to break down these stored carbohydrates to make energy available to cells . Both animals and plants temporarily store the released energy in the form of high energy molecules, such as ATP, for use in various cellular processes . </P> <P> Although humans consume a variety of carbohydrates, digestion breaks down complex carbohydrates into a few simple monomers (monosaccharides) for metabolism: glucose, fructose, and galactose . Glucose constitutes about 80% of the products, and is the primary structure that is distributed to cells in the tissues, where it is broken down or stored as glycogen . In aerobic respiration, the main form of cellular respiration used by humans, glucose and oxygen are metabolized to release energy, with carbon dioxide and water as byproducts . Most of the fructose and galactose travel to the liver, where they can be converted to glucose . </P> <P> Some simple carbohydrates have their own enzymatic oxidation pathways, as do only a few of the more complex carbohydrates . The disaccharide lactose, for instance, requires the enzyme lactase to be broken into its monosaccharide components, glucose and galactose . </P> <P> Glycolysis is the process of breaking down a glucose molecule into two pyruvate molecules, while storing energy released during this process as ATP and NADH . Nearly all organisms that break down glucose utilize glycolysis . Glucose regulation and product use are the primary categories in which these pathways differ between organisms . In some tissues and organisms, glycolysis is the sole method of energy production . This pathway is anaerobic, because it doesn't require oxygen . </P>

Discuss the regulation of glucose metabolism in the body